#4 Check return codes everywhere

[Markus Elfring]

Some checks for return codes are missing.

Examples:
1. Would you like to add more error handling for return values from "pthread_mutex_lock" like in the function "writePixmapToLCD"?
http://g15tools.svn.sourceforge.net/viewvc/g15tools/trunk/libg15/libg15.c?revision=224&view=markup

2. The file "wbmp_fd" is not closen by the function "g15r_loadWbmpToBuf" if an memory allocation failed.
http://g15tools.svn.sourceforge.net/viewvc/g15tools/trunk/libg15render/pixel.c?revision=227&view=markup