GlrawTextureLoader cannot load texture with file suffixes

[sbusch42]

When converting "gloperate-logo.png" into a glraw texture, the default output name was "gloperate-logo.501.168.rgba.ub.glraw". This file could not be loaded with GlrawTextureLoader, propably because the detected suffix contains more than just ".glraw".

Fix GlrawTextureLoader to accept all ".glraw" and ".raw" files, regardless of how many periods the filename may include.