checkasm: looprestoration: Do strict bounds checking of the output

This would allow to immediately detect unintended writes out of bounds like the ones fixed in 72b53807 and 1c7433a5.

Extend the PIXEL_RECT macro to provide a variable containing the full, padded height of the buffer, for uses that operate on the full buffer.

Allow overwriting past the right edge of the target output rectangle, up to an alignment of 64 pixels, but allow no overwrite past the bottom.