Editor: hide old proposal if new proposal is empty

amends 28447355ba

Change-Id: Ica1b95e205be4328e675714dbf81f813a76ec9a3
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/texteditor/codeassist/codeassistant.cpp

@@ -337,6 +337,7 @@ void CodeAssistantPrivate::displayProposal(IAssistProposal *newProposal, AssistR
     if (!newProposal->hasItemsToPropose(prefix, reason)) {
         if (newProposal->isCorrective(m_editorWidget))
             newProposal->makeCorrection(m_editorWidget);
+        destroyContext();
         return;
     }