BUG/MINOR: lua: Properly catch alloc errors when parsing lua filter directives

BUG/MINOR: lua: Properly catch alloc errors when parsing lua filter directives

When a lua filter declaration is parsed, some allocation errors were not
properly handled. In addition, we must be sure the filter identifier is defined
in lua to duplicate it when the filter configuration is filled.

This patch fix a defect reported in the issue #1347. It only concerns
2.5-dev. No backport needed.