skins: fix crash if input-title-format is empty

(cherry picked from commit 541b381c676cc96b6e1967610a2077b00950b86d)

modules/gui/skins2/src/vlcproc.cpp

@@ -738,9 +738,15 @@ void VlcProc::update_current_input()
     {
         // Update short name (as defined by --input-title-format)
         char *psz_fmt = var_InheritString( getIntf(), "input-title-format" );
-        char *psz_name = str_format_meta( pInput, psz_fmt );
-        SET_TEXT( m_cVarStreamName, UString( getIntf(), psz_name ) );
+        char *psz_name = NULL;
+        if( psz_fmt != NULL )
+        {
+            psz_name = str_format_meta( pInput, psz_fmt );
             free( psz_fmt );
+        }
+
+        SET_TEXT( m_cVarStreamName, UString( getIntf(),
+                                             psz_name ? psz_name : "" ) );
         free( psz_name );
 
         // Update local path (if possible) or full uri