HPCC-11284 Assert failure on certain (unusual) file names in Roxie queries

File names that might be accepted by dali but which contain characters that
are not accepted in an xpath will cause asserts in Roxie's local cache of dali
information

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
HPCC-11284 Assert failure on certain (unusual) file names in Roxie queries

Make sure that the xpath used always starts with a valid alpha character.

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge pull request #5761 from richardkchapman/roxie-assert-filecache

HPCC-11284 Assert failure on certain (unusual) file names in Roxie queries

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>