Correctly check for the case where we didn't find the mpool that we

were looking for.  This makes the openib btl fail a little more
gracefully (for example) if you specify a bogus value to
btl_openib_mpool.

Thanks to Roberto Ammendola for identifying the exact issue.

This commit was SVN r21044.

ompi/mca/mpool/base/mpool_base_lookup.c

@@ -82,7 +82,7 @@ mca_mpool_base_module_t* mca_mpool_base_module_create(
          }
     }
 
-    if (NULL == component) {
+    if (opal_list_get_end(&mca_mpool_base_components) == item) {
         return NULL;
     }
     module = component->mpool_init(resources);