Possible panic with index out of bounds if a Frame in animated WEBP is bigger or offset with bounds is larger than the canvas

[arskov]

From the discussion in #1959, the code in extended.rs#266 can go out of bound if frame's bounds + offset become larger than the whole image's canvas.

Expected

Implement a cropping logic in the loop around extended.rs#266 which will check if the drawing point goes out of bounds then the corresponding x/y loop should break and continue from the next line.

[arskov]

Fixed with #1961