Editor: Fix null-pointer dereference

Task-number: QTCREATORBUG-7330
Change-Id: I5c76e5ce4e3ab7f0659a7df82301b853a9983da1
Reviewed-by: hjk <qthjk@ovi.com>

src/plugins/cppeditor/cppfunctiondecldeflink.cpp

@@ -197,6 +197,7 @@ static QSharedPointer<FunctionDeclDefLink> findLinkHelper(QSharedPointer<Functio
     // the parens are necessary for finding good places for changes
     if (!targetFuncDecl->lparen_token || !targetFuncDecl->rparen_token)
         return noResult;
+    QTC_ASSERT(targetFuncDecl->symbol, return noResult);
     // if the source and target argument counts differ, something is wrong
     QTC_ASSERT(targetFuncDecl->symbol->argumentCount() == link->sourceFunction->argumentCount(), return noResult);