[perl #128342] > assertion doesn't work if is zero-width

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# New Ticket Created by  Lloyd Fournier 
# Please include the string:  [perl #128342]
# in the subject line of all future correspondence about this issue. 
# <URL: https://rt.perl.org/Ticket/Display.html?id=128342 >


my token foo { .? };
say "a" ~~ /"a"<?after "a"<foo>>/

should match like this does
say "a" ~~ /"a"<?after "a".?>/

and this
my token foo { .? };
say "ab" ~~ /"ab"<?after "a"<foo>>/