s4:dsdb:strcasecmp_with_ldb_val() avoids overflow

In the unlikely event that strlen(str) > INT_MAX, the result could
have overflowed.

This is not a sort transitivity issue, as this is not a symmetric sort
comparison, but it would affect binary search reliability.

Signed-off-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>

source4/dsdb/schema/schema_query.c

@@ -52,7 +52,9 @@ static int strcasecmp_with_ldb_val(const struct ldb_val *target, const char *str
 			}
 			return 1;
 		}
-		return (target->length - len);
+		if (target->length < len) {
+			return -1;
+		}
 	}
 	return ret;
 }