Editor: delete processor after canceling

Set a null proposal has the potential to restart the processor
in combination with the invalidateCurrentRequestData from this
cancelCurrentRequest will result in a restarted processor that is not
tracked via m_asyncProcessor.

Change-Id: Ia0e0d49564170a1e705994933d07e00c23f24f5d
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/texteditor/codeassist/codeassistant.cpp

@@ -292,7 +292,7 @@ void CodeAssistantPrivate::cancelCurrentRequest()
     }
     if (m_asyncProcessor) {
         m_asyncProcessor->cancel();
-        m_asyncProcessor->setAsyncProposalAvailable(nullptr);
+        delete m_asyncProcessor;
     }
     invalidateCurrentRequestData();
 }