Handle timezone strings with strippable contents properly
Summary:
We were asserting that we would not identify a timezone id in a timezone string
if our specialized logic had not detected one earlier. This could still arise
if there were characters at the end of the timezone string that timelib strips.
See timelib's stripping behavior here:
https://github.com/derickr/timelib/blob/
00fcceca7eaf28b650755ad6e7bfe75473125705/parse_date.re#L743-L745
Reviewed By: ricklavoie
Differential Revision:
D27910402
fbshipit-source-id:
1db38b0a281edbb919d7371cf5549fe99a390cb6