Debugger: Avoid looking up qt symbols globally to get the qt namespace

This can get very expensive for targets that have a lot or big modules,
but are not linked against Qt. On the downside we might not be able to
identify Qt namespaces in static builds.

Task-number: QTCREATORBUG-18287
Change-Id: I90e0c4afcde17fd81d49017e828ce59f0abe9b5c
Reviewed-by: hjk <hjk@qt.io>
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

share/qtcreator/debugger/cdbbridge.py

@@ -304,10 +304,10 @@ class Dumper(DumperBase):
                 namespaceIndex = name.find('::')
                 if namespaceIndex > 0:
                     namespace = name[:namespaceIndex + 2]
-        self.qtNamespace = lambda: namespace
             self.qtCustomEventFunc = self.parseAndEvaluate(
                 '%s!%sQObject::customEvent' %
                 (self.qtCoreModuleName(), namespace)).address()
+        self.qtNamespace = lambda: namespace
         return namespace
 
     def qtVersion(self):