Player doesn't load a graphics file with the wrong extension

[javlag]

For example ,a bmp file named file.png won't be loaded while the RPG_RT.exe loads it. It returns "Invalid BMP file" while RPG_RT.exe solve the problem by itself without renaming the wrong file

[carstene1ns]

This is a bit related to #74.
Possible solution:
Load file like now, but add a mimetype/fileheader check, if loading fails. Then load with correct type.
This way there is no extra work done for correct files.
Or, because file has to be loaded to memory anyway:
first load file to memory, then determine file type by magic number, then pass to correct function.