reset search hits when entering empty or invalid query

filterwidget.py

@@ -123,6 +123,7 @@ class FilterWidget(QWidget):
         query = self.query_field.text()
         ignore_case = self.ignore_case.isChecked()
         if len(query) == 0:
+            self.filter_model.truncate()
             return
 
         # cancel previous search
@@ -135,7 +136,8 @@ class FilterWidget(QWidget):
             else:
                 regex = re.compile(re.escape(query), flags=flags)
         except:
-            # query was not a valid regex -> abort
+            # query was not a valid regex -> clear search hits, then abort
+            self.filter_model.truncate()
             return
 
         self.filter_task = FilterTask(