codec/libass: avoid possible segfault

dialog_ProgressCreate can return NULL. For this case,
only deal with the result if it is not NULL.
Signed-off-by: Rémi Duraffort <ivoire@videolan.org>

modules/codec/libass.c

@@ -724,6 +724,7 @@ static ass_handle_t *AssHandleHold( decoder_t *p_dec )
     ass_set_fonts_dir( p_library, psz_font_dir );
     free( psz_font_dir );
 #ifdef WIN32
+    if( p_dialog )
         dialog_ProgressSet( p_dialog, NULL, 0.1 );
 #endif
 
@@ -747,6 +748,7 @@ static ass_handle_t *AssHandleHold( decoder_t *p_dec )
 
 #ifdef HAVE_FONTCONFIG
 #ifdef WIN32
+    if( p_dialog )
         dialog_ProgressSet( p_dialog, NULL, 0.2 );
 #endif
 #if defined( LIBASS_VERSION ) && LIBASS_VERSION >= 0x00907000
@@ -755,6 +757,7 @@ static ass_handle_t *AssHandleHold( decoder_t *p_dec )
     ass_set_fonts( p_renderer, psz_font, psz_family );  // setup default font/family
 #endif
 #ifdef WIN32
+    if( p_dialog )
         dialog_ProgressSet( p_dialog, NULL, 1.0 );
 #endif
 #else
@@ -774,6 +777,7 @@ static ass_handle_t *AssHandleHold( decoder_t *p_dec )
     /* */
     vlc_mutex_unlock( &libass_lock );
 #ifdef WIN32
+    if( p_dialog )
         dialog_ProgressDestroy( p_dialog );
 #endif
     return p_ass;