Fix crash on Core::Id().toString()

Change-Id: I515c5df8480f54e49ef0873472b54459f2db5a81
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>

src/plugins/coreplugin/id.cpp

@@ -52,7 +52,9 @@ namespace Core {
 class StringHolder
 {
 public:
-    StringHolder() {}
+    StringHolder()
+        : n(0), str(0)
+    {}
 
     StringHolder(const char *s, int length)
         : n(length), str(s)