show errno not result

open_levelfile_exclusively() was showing the return value -1 in a panic message, even though that was the only possible value; show errno instead

doc/fixes34.3

@@ -21,6 +21,8 @@ do not pacify shopkeeper when the hero enters a shop if that hero previously
 	angered the shopkeeper without ever visibly entering the shop
 attempting to place migrating monsters onto a monster-saturated level no
 	longer triggers impossible()
+open_levelfile_exclusively() was showing the return value -1 in a panic message,
+	even though that was the only possible value; show errno instead
 
 
 Platform- and/or Interface-Specific Fixes

src/files.c

@@ -550,7 +550,7 @@ int lev, oflag;
 			fd = lftrack.fd;
 			reslt = lseek(fd, 0L, SEEK_SET);
 			if (reslt == -1L)
-			    panic("open_levelfile_exclusively: lseek failed %d", reslt);
+			    panic("open_levelfile_exclusively: lseek failed %d", errno);
 			lftrack.nethack_thinks_it_is_open = TRUE;
 		} else {
 			really_close();