qt: fix subtitle path not encoded properly in open panel

:sub-file doesn't accept URL
Signed-off-by: Hugo Beauzée-Luyssen <hugo@beauzee.fr>
(cherry picked from commit 143b6e32)
Signed-off-by: Hugo Beauzée-Luyssen <hugo@beauzee.fr>

modules/gui/qt/components/open_panels.cpp

@@ -287,7 +287,7 @@ void FileOpenPanel::updateMRL()
 
     /* Options */
     if( ui.subGroupBox->isChecked() &&  !subUrl.isEmpty() ) {
-        mrl.append( " :sub-file=" + colon_escape( subUrl.toEncoded() ) );
+        mrl.append( " :sub-file=" + colon_escape( subUrl.toLocalFile() ) );
     }
 
     emit methodChanged( "file-caching" );