Exit correctly from PrepareRedoRemove() when not found

Complex crash bug all started with this failure.
Diagnosed and fixed by Nikhil Sontakke, reviewed by me.

Reported-by: Jeff Janes
Author: Nikhil Sontakke
Discussion: https://postgr.es/m/CAMkU=1xBP8cqdS5eK8APHL=X6RHMMM2vG5g+QamduuTsyCwv9g@mail.gmail.com

src/backend/access/transam/twophase.c

@@ -2375,6 +2375,7 @@ PrepareRedoRemove(TransactionId xid, bool giveWarning)
 {
 	GlobalTransaction gxact = NULL;
 	int			i;
+	bool		found = false;
 
 	Assert(RecoveryInProgress());
 
@@ -2386,6 +2387,7 @@ PrepareRedoRemove(TransactionId xid, bool giveWarning)
 		if (gxact->xid == xid)
 		{
 			Assert(gxact->inredo);
+			found = true;
 			break;
 		}
 	}
@@ -2394,7 +2396,7 @@ PrepareRedoRemove(TransactionId xid, bool giveWarning)
 	/*
 	 * Just leave if there is nothing, this is expected during WAL replay.
 	 */
-	if (gxact == NULL)
+	if (!found)
 		return;
 
 	/*