gui/qt: info_panels: fix leak + potential null-dereference

vlc_meta_CopyExtraNames returns a pointer to a dynamically allocated
resource, this should of course be cleaned up after it is used; we
should also not assume that the function is always successful, but
instead check to see that we really have data to use in order to
prevent *undefined-behavior*.

CID: #1401545
Signed-off-by: Hugo Beauzée-Luyssen <hugo@beauzee.fr>

modules/gui/qt/components/info_panels.cpp

@@ -440,11 +440,15 @@ void ExtraMetaPanel::update( input_item_t *p_item )
         add_row( VLC_META_DISCNUMBER, psz_disc );
 
     char ** ppsz_keys = vlc_meta_CopyExtraNames( p_meta );
-
-    for( int i = 0; ppsz_keys[i]; ++i )
+    if( ppsz_keys )
     {
-        add_row( ppsz_keys[i], vlc_meta_GetExtra( p_meta, ppsz_keys[i] ) );
-        free( ppsz_keys[i] );
+        for( int i = 0; ppsz_keys[i]; ++i )
+        {
+            add_row( ppsz_keys[i], vlc_meta_GetExtra( p_meta, ppsz_keys[i] ) );
+            free( ppsz_keys[i] );
+        }
+
+        free( ppsz_keys );
     }
 
     extraMeta->verticalHeader()->resizeSections( QHeaderView::ResizeToContents );