php: Out-of-bound read in timelib_meridian()

In PHP before 5.6.32, 7.x before 7.0.25, and 7.1.x before 7.1.11, an error in the date extension's timelibmeridian handling of 'front of' and 'back of' directives could be used by attackers able to supply date strings to leak information from the interpreter, related to ext/date/lib/parsedate.c...