[FIX] header_custom_less: Don't delete the theme file if there's an error, delete the corrupted or empty custom css file instead
[FIX] header_custom_less: Don't delete the theme file if there's an error, delete the corrupted or empty custom css file instead

git-svn-id: a7fabbc6a7c54ea5c67cbd16bd322330fd10cc35@56869 b456876b-0849-0410-b77d-98878d47e9d5

oregional/tiki,oregional/tiki,oregional/tiki,tikiorg/tiki,oregional/tiki,tikiorg/tiki,tikiorg/tiki,tikiorg/tiki