CppTools: Fix crash on document close

Emit the signal only if we are not canceled.

Task-number: QTCREATORBUG-17249
Change-Id: I5082a5fe7554eecdc7ec5d148150c1b169002f6d
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/cpptools/cppchecksymbols.cpp

@@ -346,9 +346,9 @@ void CheckSymbols::run()
             _usages << QVector<Result>::fromList(_macroUses);
             flush();
         }
-    }
 
-    emit codeWarningsUpdated(_doc, _diagMsgs);
+        emit codeWarningsUpdated(_doc, _diagMsgs);
+    }
 
     reportFinished();
 }