Fix a bug that caused the system to crash when asked for an index of the segment names. Such a request required passing a NULL value for the segment name, but the find_seg function didn't protect itself from that value.

Thanks to James Kennedy (UCC-Ireland) for finding it.

This commit was SVN r10847.

orte/mca/gpr/replica/transition_layer/gpr_replica_segment_tl.c

@@ -44,6 +44,15 @@ int orte_gpr_replica_find_seg(orte_gpr_replica_segment_t **seg,
     /* initialize to nothing */
     *seg = NULL;
     
+    if (NULL == segment) {
+        /* this is an allowed value - the index function, for example,
+         * will pass this to us if we want the index of the global level
+         * of the registry (i.e., the index of segment names). Just return
+         * NULL and we'll be okay
+         */
+        return ORTE_SUCCESS;
+    }
+    
     len = strlen(segment);
 
     /* search the registry segments to find which one is being referenced */