Clang: Prevent segmentation fault in WriteMessageBlock

There could be already messages send before the backend is available. In
that case we now record that messages and send them if the socket is set.

Task-number: QTCREATORBUG-19761
Change-Id: I7c8d6fdb4fcc043bcdbb9e9aeb5752f89c24fdab
Reviewed-by: Ivan Donchevskii <ivan.donchevskii@qt.io>

src/libs/clangsupport/connectionclient.h

@@ -89,7 +89,7 @@ protected:
     LinePrefixer &stdOutPrefixer();
 
     virtual void sendEndCommand() = 0;
-    virtual void resetCounter() = 0;
+    virtual void resetState() = 0;
     virtual QString outputName() const = 0;
 
     QString connectionName() const;