Fix for grammar parser returning MATCH_END when partial match items exist

[emcgee]

Updates to match corresponding change in FreeSWITCH mod_rayo: https://stash.freeswitch.org/projects/FS/repos/freeswitch/commits/28bc992fcedbdf7814556074da856944fcbd9bfe#src/mod/event_handlers/mod_rayo/srgs.c

[benlangfeld]

Could we add test cases similar to those in the FS change to demonstrate the issue?

[benlangfeld]

Also, a rebase on the current develop branch for a passing test suite would be awesome :)

[emcgee]

Rebased, although entirely unsure of how to add an appropriate spec for this based on the SRGS tests in FS.

[coveralls]

Coverage increased (+1.08%) to 99.055% when pulling 1c72ef1 on ringplus:develop into 5756254 on adhearsion:develop.