Clang: Fix memory leak on completion

Leak happened if the user triggered the completion again, before the
results for the first completion arrived.

Side note: This is one more reason for using smart pointers to manage
code assist objects.

Change-Id: I582d364286ca47f8622383f3365ad4e5933eb2df
Reviewed-by: Erik Verbruggen <erik.verbruggen@theqtcompany.com>

src/plugins/texteditor/codeassist/codeassistant.cpp

@@ -34,6 +34,7 @@
 #include "iassistprocessor.h"
 #include "textdocument.h"
 #include "iassistproposal.h"
+#include "iassistproposalmodel.h"
 #include "iassistproposalwidget.h"
 #include "assistinterface.h"
 #include "assistproposalitem.h"
@@ -263,8 +264,11 @@ void CodeAssistantPrivate::requestProposal(AssistReason reason,
     case IAssistProvider::Asynchronous: {
         processor->setAsyncCompletionAvailableHandler(
             [this, processor, reason](IAssistProposal *newProposal){
-                if (m_asyncProcessor != processor)
+                if (m_asyncProcessor != processor) {
+                    delete newProposal->model();
+                    delete newProposal;
                     return;
+                }
 
                 invalidateCurrentRequestData();
                 QTC_CHECK(newProposal);