Fix a thinko introduced into CountActiveBackends by a recent patch:

we should ignore NULL array entries, not non-NULL ones.  This had the
effect of disabling commit_delay, and could have caused a crash in the
rare race condition the patch was intended to fix.

Bug report and diagnosis by Jeff Janes, in bug #4952.

src/backend/storage/ipc/procarray.c

@@ -23,7 +23,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/storage/ipc/procarray.c,v 1.50 2009/06/11 14:49:02 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/storage/ipc/procarray.c,v 1.51 2009/07/29 15:57:11 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1137,7 +1137,7 @@ CountActiveBackends(void)
 		 * free list and are recycled. Its contents are nonsense in that case,
 		 * but that's acceptable for this function.
 		 */
-		if (proc != NULL)
+		if (proc == NULL)
 			continue;
 
 		if (proc == MyProc)