BUG/MINOR: hlua_fcn: fix broken yield for Patref:add_bulk()

BUG/MINOR: hlua_fcn: fix broken yield for Patref:add_bulk()

In GH #3241, GH user @kanashimia reported that the Patref:add_bulk()
method would raise a Lua exception when called with more than 101
elements at once.

As identified by @kanashimia there was an error in the way the
add_bulk() method was forced to yield after 101 elements precisely.
The yield is there to ensure Lua doesn't eat too much ressources at
once and doesn't impact haproxy's core responsiveness, but the check
for the yield was misplaced resulting in improper stack content upon
resume.

Thanks to user @kanashimia who even provided a reproducer which helped
a lot to troubleshoot the issue.

This fix should be backported up to 3.2 with 884dc62 ("MINOR: hlua_fcn:
add Patref:add_bulk()") where the bug was introduced.