[lua] Fix bug in genlua causing significant slowdown in all loops. #11453
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The condition on line 585 was missing a begin/end block so the generator was unconditionally modifying a variable named
_hx_do_first_*which was supposed to only exist for do-while loops.Since the code that initializes
_hx_do_first_*doesn't have this problem, no local variable is created, which means that this bug causes a global variable access for every iteration of every non do-while loop (very bad for performance). Fixing this improved the performance of loops by about 30% in my limited testing. They are now the same speed as writing a loop in Lua by hand.