If we don't have a backup-end-location, don't claim we've reached it.

This was apparently a typo, which caused recovery to think that it
immediately reached the end of backup, and allowed the database to start
up too early.

Reported by Jeff Janes. Backpatch to 9.2, where this code was introduced.

Author: hlinnaka

src/backend/access/transam/xlog.c

@@ -5859,7 +5859,7 @@ StartupXLOG(void)
 				/* Pop the error context stack */
 				error_context_stack = errcallback.previous;
 
-				if (!XLogRecPtrIsInvalid(ControlFile->backupStartPoint) &&
+				if (!XLogRecPtrIsInvalid(ControlFile->backupEndPoint) &&
 					XLByteLE(ControlFile->backupEndPoint, EndRecPtr))
 				{
 					/*