Multiple divide-by-zero sites potentially causing crashes

[dns43]

In lodepng_deflatev(), getPixelColorsRGBA8() and lodepng_convert_rgb(), divide by zero can be triggered via bitdepth and input size. Please check if greater than 0 before usage.

LOC enumaration:
https://sourcegraph.com/github.com/lvandeve/lodepng@master/-/blob/lodepng.cpp#L3271
https://sourcegraph.com/github.com/lvandeve/lodepng@master/-/blob/lodepng.cpp#L3355
https://sourcegraph.com/github.com/lvandeve/lodepng@master/-/blob/lodepng.cpp#L3443:17
https://sourcegraph.com/github.com/lvandeve/lodepng@master/-/blob/lodepng.cpp#L3610
https://sourcegraph.com/github.com/lvandeve/lodepng@7fdcc96a5e5864eee72911c3ca79b1d9f0d12292/-/blob/lodepng.cpp#L2093

Happy to provide PoC