Return value of lseek() can be negative on failure.

Because the return value of lseek() was assigned to an unsigned size_t
variable, we'd fail to notice an error return code -1. Compiler gave a
warning about this.

Andres Freund

src/backend/replication/walsender.c

@@ -315,8 +315,8 @@ SendTimeLineHistory(TimeLineHistoryCmd *cmd)
 	char		histfname[MAXFNAMELEN];
 	char		path[MAXPGPATH];
 	int			fd;
-	size_t		histfilelen;
-	size_t		bytesleft;
+	off_t		histfilelen;
+	off_t		bytesleft;
 
 	/*
 	 * Reply with a result set with one row, and two columns. The first col