fix Array#delete always firing the block when deleting nil

[phi-luna]

reimplement Array#delete in c, fixing ary.delete(nil, &blk) firing the block regardless of removal

minimal reproduction:

ary = [nil]
ret = ary.delete(nil) { "not deleted?" }

result on master:

ret
# => "not deleted?"
ary
# => []

result after this patch:

ret 
# => nil
ary
# => []

[matz]

Thanks for the PR. But as a principle, the mruby standard library does not call blocks from C code unless absolutely necessary (to avoid VM recursion). I do not consider it an absolute necessity this time.
We have several options:

• After PR merge, I will modify it not to call the block
• I fix the Ruby code
• @leviongit will update the PR

Which is your preference?

[phi-luna]

thank you for the comment. i will amend the pr.

[matz]

I that case, you can implement the body part in C (which probably returns index or - 1; you may name it __delete), or you can fix the Ruby code.

[phi-luna]

i will check whether implementing the core part in c is worthwhile and will come back with results

edit:
i believe it is worthwhile (and it was fairly easy to do so)

[phi-luna]

this pr is ready to merge

[matz]

Thank you!