syncqt: Fix -help option

Skip sanity checks if a -help option is detected.
Otherwise, syncqt bails out with e.g.

   You need to specify either -headers or -all option.

Change-Id: I49eee48cd1825244cb6d04152734cb0dfa03fc5f
Reviewed-by: Alexey Edelev <alexey.edelev@qt.io>

src/tools/syncqt/main.cpp

@@ -348,6 +348,9 @@ private:
             }
         }
 
+        if (m_printHelpOnly)
+            return true;
+
         if (!qpaHeadersFilter.empty())
             m_qpaHeadersRegex = std::regex(qpaHeadersFilter);