reset filter only after cancelling the search

Fixes issue where the UI froze when removing the last char of a query while still a search was running. This caused the search thread to append to the newly truncated file, resulting in megabytes of null bytes at the beginning.

filterwidget.py

@@ -43,11 +43,6 @@ class FilterTask(QRunnable):
             # print("starting thread ", threading.currentThread())
             self.on_before()
 
-            # delay the filtering. This work arounds a race condition. For some reasons, even though we have locks
-            # to ensure that only one thread writes to the target file, it happened that the file was not correctly
-            # truncated and started with null bytes. Sometimes several MB of null bytes. My guess is that this is
-            # caused by async write operations.
-            time.sleep(0.5)
             if self.aborted:
                 self.on_finish()
 
@@ -160,13 +155,14 @@ class FilterWidget(QWidget):
         query = self.query_field.text()
         ignore_case = self.ignore_case.isChecked()
         is_regex = self.is_regex.isChecked()
-        if len(query) == 0:
-            self.reset_filter()
-            return
 
         # cancel previous search
         self._cancel_search()
 
+        if len(query) == 0:
+            self.reset_filter()
+            return
+
         try:
             flags = re.IGNORECASE if ignore_case else 0
             if is_regex: