qt4: add webm on convert containers list

(cherry picked from commit 2fddd625)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/gui/qt4/dialogs/convert.cpp

@@ -110,7 +110,7 @@ void ConvertDialog::fileBrowse()
 {
     QString fileName = QFileDialog::getSaveFileName( this, qtr( "Save file..." ),
             "",
- qtr( "Containers (*.ps *.ts *.mpg *.ogg *.asf *.mp4 *.mov *.wav *.raw *.flv)" ) );
+ qtr( "Containers (*.ps *.ts *.mpg *.ogg *.asf *.mp4 *.mov *.wav *.raw *.flv *.webm)" ) );
     fileLine->setText( toNativeSeparators( fileName ) );
 }