Suggestion: Open and Find should return errors

[SirRFI]

• bitmap version (or commit ref): v0.10.0-beta3.1
• Go version: go version go1.17.6 windows/amd64
• Gcc version: gcc.exe (x86_64-win32-seh-rev0, Built by MinGW-W64 project) 8.1.0 (recommended by robotgo's README)
• Operating system and bit: Windows 10 64bit
• Provide example code:

package main

import (
	"fmt"
	"github.com/vcaesar/bitmap"
)

func main() {
	img := bitmap.Open("iDontExist.png") // nil
	x, y := bitmap.Find(img)
	fmt.Println(x, y) // -1 -1
}

go run .
bitmap is not ready yet!
-1 -1

Description

Open, Find and maybe some other functions should return an error on failure.
Currently "bitmap is not ready yet!" appears in output during attempt to find invalid? bitmap. on the screen.
Even with valid "needle" (image to be searched for) was provided, but simply not found in "haystack" (image to be searched in), it will return -1 for both X and Y, which actually can be valid position in multi-screen setup, as shown here.

Initially suggested here.