Fixed a reference to uninitialized memory

This was only found with _GLIBCXX_DEBUG=1 *and* coverage analysis
(-fprofile-arcs -ftest-coverage).

src/iterators.h

@@ -99,7 +99,7 @@ public:
   }
 
   virtual post_t * operator()() {
-    if (posts_i == posts_end || posts_uninitialized)
+    if (posts_uninitialized || posts_i == posts_end)
       return NULL;
     return *posts_i++;
   }