QmakeProject: Do not try to emit "parsingStarted" several times

This prevents a soft assert from triggering.

Change-Id: Ic2b650f1c850d87492bad8f23d200ede0de35722
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@qt.io>
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/plugins/qmakeprojectmanager/qmakeproject.cpp

@@ -478,7 +478,9 @@ void QmakeProject::scheduleAsyncUpdate(QmakeProFile::AsyncUpdateDelay delay)
         return;
     }
 
-    emitParsingStarted();
+    if (m_asyncUpdateState != Base)
+        emitParsingStarted();
+
     rootProFile()->setParseInProgressRecursive(true);
     setAllBuildConfigurationsEnabled(false);