handle unset setting values in processing (fixes #11340)

Author: jef-n

python/plugins/processing/gui/ConfigDialog.py

@@ -229,6 +229,8 @@ def eventFilter(self, editor, event):
         return QStyledItemDelegate.eventFilter(self, editor, event)
 
     def convertValue(self, value):
+	if value is None:
+            return ""
         try:
             return int(value)
         except ValueError: