Set VideoWidget minimal size to 16x16 (I'm not sure it is the right thing).

It avoids segfault when resizing to 0x0.
It fixes segfault when VLC is started with a video file. (But I fear
that we have a race condition here because if the same file is played
later, it works)

modules/gui/qt4/components/interface_widgets.cpp

@@ -91,7 +91,7 @@ void *VideoWidget::request( vout_thread_t *p_nvout, int *pi_x, int *pi_y,
         return NULL;
     }
     p_vout = p_nvout;
-    setMinimumSize( 0, 0 );
+    setMinimumSize( 16, 16 );
     return (void*)winId();
 }