[master] added missing initialization

the original version didn't have a problem because the constructor
should never be used in python wrappers, but I do this to silence cppcheck.
the change is small anyway.

src/lib/python/isc/datasrc/updater_python.cc

@@ -203,7 +203,7 @@ namespace {
 
 class s_UpdaterRRsetCollection : public s_RRsetCollection {
 public:
-    s_UpdaterRRsetCollection() : s_RRsetCollection() {}
+    s_UpdaterRRsetCollection() : s_RRsetCollection(), base_obj_(NULL) {}
     PyObject* base_obj_;
 };