Fix memory issues on freeverb side

[falkTX]

As detected by valgrind.
Related log:

==860999== Conditional jump or move depends on uninitialised value(s)
==860999==    at 0xC77AA2: ASrevmodel::update() (revmodel.cpp:141)
==860999==    by 0xC77C7E: ASrevmodel::setwet(float) (revmodel.cpp:190)
==860999==    by 0xC7774A: ASrevmodel::init(float) (revmodel.cpp:76)
==860999==    by 0xC1C892: ReverbFx::ReverbFx() (Reverb.cpp:78)
==860999==    by 0xC1E493: rack::CardinalPluginModel<ReverbFx, ReverbFxWidget>::createModule() (helpers.hpp:52)
==860999==    by 0x6B39D9: CardinalDISTRHO::CardinalUI::uiIdle() (CardinalUI.cpp:484)
==860999==    by 0x6CA0FA: CardinalDISTRHO::UIExporter::plugin_idle() (DistrhoUIInternal.hpp:248)
==860999==    by 0x6C6368: CardinalDISTRHO::runSelfTests() (DistrhoPluginJACK.cpp:861)
==860999==    by 0x6C65AC: main (DistrhoPluginJACK.cpp:963)
==860999==  Uninitialised value was created by a heap allocation
==860999==    at 0x6E8E013: operator new(unsigned long) (in /usr/libexec/valgrind/vgpreload_memcheck-amd64-linux.so)
==860999==    by 0xC1E488: rack::CardinalPluginModel<ReverbFx, ReverbFxWidget>::createModule() (helpers.hpp:52)
==860999==    by 0x6B39D9: CardinalDISTRHO::CardinalUI::uiIdle() (CardinalUI.cpp:484)
==860999==    by 0x6CA0FA: CardinalDISTRHO::UIExporter::plugin_idle() (DistrhoUIInternal.hpp:248)
==860999==    by 0x6C6368: CardinalDISTRHO::runSelfTests() (DistrhoPluginJACK.cpp:861)
==860999==    by 0x6C65AC: main (DistrhoPluginJACK.cpp:963)
==860999== 

==866681== Mismatched free() / delete / delete []
==866681==    at 0x6E908AF: operator delete(void*) (in /usr/libexec/valgrind/vgpreload_memcheck-amd64-linux.so)
==866681==    by 0xC77E1C: AScomb::makebuffer(float*, int) (comb.hpp:31)
==866681==    by 0xC773ED: ASrevmodel::init(float) (revmodel.cpp:48)
==866681==    by 0xC1CBA1: ReverbFx::onSampleRateChange() (Reverb.cpp:91)
==866681==    by 0x770346: rack::engine::Module::onSampleRateChange(rack::engine::Module::SampleRateChangeEvent const&) (Module.hpp:409)
==866681==    by 0x24A46AD: rack::engine::Engine::addModule(rack::engine::Module*) (Engine.cpp:616)
==866681==    by 0x6B3B5F: CardinalDISTRHO::CardinalUI::uiIdle() (CardinalUI.cpp:495)
==866681==    by 0x6CA0FA: CardinalDISTRHO::UIExporter::plugin_idle() (DistrhoUIInternal.hpp:248)
==866681==    by 0x6C6368: CardinalDISTRHO::runSelfTests() (DistrhoPluginJACK.cpp:861)
==866681==    by 0x6C65AC: main (DistrhoPluginJACK.cpp:963)
==866681==  Address 0x9c10030 is 0 bytes inside a block of size 4,464 alloc'd
==866681==    at 0x6E8F2F3: operator new[](unsigned long) (in /usr/libexec/valgrind/vgpreload_memcheck-amd64-linux.so)
==866681==    by 0xC77E43: AScomb::makebuffer(float*, int) (comb.hpp:32)
==866681==    by 0xC773ED: ASrevmodel::init(float) (revmodel.cpp:48)
==866681==    by 0xC1C892: ReverbFx::ReverbFx() (Reverb.cpp:78)
==866681==    by 0xC1E493: rack::CardinalPluginModel<ReverbFx, ReverbFxWidget>::createModule() (helpers.hpp:52)
==866681==    by 0x6B39D9: CardinalDISTRHO::CardinalUI::uiIdle() (CardinalUI.cpp:484)
==866681==    by 0x6CA0FA: CardinalDISTRHO::UIExporter::plugin_idle() (DistrhoUIInternal.hpp:248)
==866681==    by 0x6C6368: CardinalDISTRHO::runSelfTests() (DistrhoPluginJACK.cpp:861)
==866681==    by 0x6C65AC: main (DistrhoPluginJACK.cpp:963)
==866681== 

==867243== Mismatched free() / delete / delete []
==867243==    at 0x6E908AF: operator delete(void*) (in /usr/libexec/valgrind/vgpreload_memcheck-amd64-linux.so)
==867243==    by 0xC77FF6: ASallpass::makebuffer(float*, int) (allpass.hpp:29)
==867243==    by 0xC7762F: ASrevmodel::init(float) (revmodel.cpp:65)
==867243==    by 0xC1CBA9: ReverbFx::onSampleRateChange() (Reverb.cpp:91)
==867243==    by 0x770346: rack::engine::Module::onSampleRateChange(rack::engine::Module::SampleRateChangeEvent const&) (Module.hpp:409)
==867243==    by 0x24A46BD: rack::engine::Engine::addModule(rack::engine::Module*) (Engine.cpp:616)
==867243==    by 0x6B3B5F: CardinalDISTRHO::CardinalUI::uiIdle() (CardinalUI.cpp:495)
==867243==    by 0x6CA0FA: CardinalDISTRHO::UIExporter::plugin_idle() (DistrhoUIInternal.hpp:248)
==867243==    by 0x6C6368: CardinalDISTRHO::runSelfTests() (DistrhoPluginJACK.cpp:861)
==867243==    by 0x6C65AC: main (DistrhoPluginJACK.cpp:963)
==867243==  Address 0x9c1b040 is 0 bytes inside a block of size 2,224 alloc'd
==867243==    at 0x6E8F2F3: operator new[](unsigned long) (in /usr/libexec/valgrind/vgpreload_memcheck-amd64-linux.so)
==867243==    by 0xC7801D: ASallpass::makebuffer(float*, int) (allpass.hpp:30)
==867243==    by 0xC7762F: ASrevmodel::init(float) (revmodel.cpp:65)
==867243==    by 0xC1C89A: ReverbFx::ReverbFx() (Reverb.cpp:78)
==867243==    by 0xC1E49B: rack::CardinalPluginModel<ReverbFx, ReverbFxWidget>::createModule() (helpers.hpp:52)
==867243==    by 0x6B39D9: CardinalDISTRHO::CardinalUI::uiIdle() (CardinalUI.cpp:484)
==867243==    by 0x6CA0FA: CardinalDISTRHO::UIExporter::plugin_idle() (DistrhoUIInternal.hpp:248)
==867243==    by 0x6C6368: CardinalDISTRHO::runSelfTests() (DistrhoPluginJACK.cpp:861)
==867243==    by 0x6C65AC: main (DistrhoPluginJACK.cpp:963)
==867243==