Correctly reject bad tftp addresses earlier, rather than later.

This check is for end == NULL but was meant to be *end == '\0'.  Without
this change, we'll pass a plausibly bad address (i.e. one with no ']' at
the end) to Mtftp(... READ_FILE ...), which should fail correctly, but
our error messaging will be inconsistent.

Signed-off-by: Peter Jones <pjones@redhat.com>

netboot.c

@@ -234,7 +234,7 @@ static BOOLEAN extract_tftp_info(CHAR8 *url)
 			return FALSE;
 		}
 	}
-	if (end == '\0') {
+	if (*end == '\0') {
 		Print(L"TFTP SERVER MUST BE ENCLOSED IN [..]\n");
 		return FALSE;
 	}