When a bgworker exits, always call ReleasePostmasterChildSlot.

Commit e2ce9aa27b was insufficiently
well thought out.  Repair.

src/backend/postmaster/postmaster.c

@@ -2856,23 +2856,25 @@ CleanupBackgroundWorker(int pid,
 		 * backend, any exit status other than 0 or 1 is considered a crash
 		 * and causes a system-wide restart.
 		 */
-		if (rw->rw_worker.bgw_flags & BGWORKER_SHMEM_ACCESS)
+		if ((rw->rw_worker.bgw_flags & BGWORKER_SHMEM_ACCESS) != 0)
 		{
 			if (!EXIT_STATUS_0(exitstatus) && !EXIT_STATUS_1(exitstatus))
 			{
 				HandleChildCrash(pid, exitstatus, namebuf);
 				return true;
 			}
+		}
 
-			if (!ReleasePostmasterChildSlot(rw->rw_child_slot))
-			{
-				/*
-				 * Uh-oh, the child failed to clean itself up.  Treat as a
-				 * crash after all.
-				 */
-				HandleChildCrash(pid, exitstatus, namebuf);
-				return true;
-			}
+		/*
+		 * We must release the postmaster child slot whether this worker
+		 * is connected to shared memory or not, but we only treat it as
+		 * a crash if it is in fact connected.
+		 */
+		if (!ReleasePostmasterChildSlot(rw->rw_child_slot) &&
+			(rw->rw_worker.bgw_flags & BGWORKER_SHMEM_ACCESS) != 0)
+		{
+			HandleChildCrash(pid, exitstatus, namebuf);
+			return true;
 		}
 
 		/* Get it out of the BackendList and clear out remaining data */