Fix PDF viewer not to produce garbage windows for nonexistent files
Fix PDF viewer not to produce garbage windows for nonexistent files

Was calling window_flush() on redraw handler which already happens on
window redrawing.

mchalupa/weston,Tarnyko/weston-xdg_surface_present,sir-murray/weston,krezovic/weston,xorgy/weston,udoprog/weston,Gnurou/weston,eyolfson/weston,giucam/weston,Fantu/compositor-spice,Fantu/compositor-spice,kwm81/weston,mchalupa/weston,Gnurou/weston,giucam/weston,xorgy/weston,sir-murray/weston,jonnylamb/weston,jonnylamb/weston,Fantu/compositor-spice,eyolfson/weston,udoprog/weston,Tarnyko/weston-xdg_surface_present,krezovic/weston,kwm81/weston