Add av_uninit to variable declarations to fix the false positive warnings:
vhook/ppm.c:236: warning: 'out_height' may be used uninitialized in this function
vhook/ppm.c:235: warning: 'out_width' may be used uninitialized in this function
patch by Patrik Kullman, patrik yes nu

Originally committed as revision 17223 to svn://svn.ffmpeg.org/ffmpeg/trunk
