CrossServer extraction source when used with $g reports 'could not find table' if the guid starts with a number

[tznind]

Describe the bug
ExecuteCrossServerDatasetExtractionSource has a field TemporaryTableName that defaults to $g.

At runtime a guid is allocated if the pattern contains '$g'. If that guid starts with a number e.g. 123ab254 then it is not a valid table name. DataTableUploadDestination recognises this and appends an underscore (i.e. it creates a table _123ab254 but then the ExecuteCrossServerDatasetExtractionSource complains that it asked for the table to be created but then the table didnt exist (because it expects it to still be called 123ab254)

The workaround is to change the TemporaryTableName pattern to _$g

The fix is probably to always put an underscore at the front or trim leading digits from the guid.