Fix known BMP reading issues

Some vendors may add invalid image size to uncompressed bitmaps, which should be 0. This size can be ignored as some bitmaps are breaking Player and working with RPG_RT.

Also, bitmaps with colorspace information (BMP version 4.x) have a larger info header (108 bytes instead of 40 bytes). These BMP files are supported by RPG_RT, so is worth to ignore the fixed info header size check and read the palette after the reported info header size instead.