Disable str($# + 1)

[mmisono]

Although str($#) is already disabled in the semantic analyzer, it's done
in the final pass. So, str($#+1) tries to do Binop analysis and
std::out_of_range error occurs. I think the check does not need to be
done in the final pass, so simply check this in all passes.

This fixes the following errors:

% sudo ./src/bpftrace -e 'BEGIN { printf("%s", str($# + 1)); exit();}' aaa
terminate called after throwing an instance of 'std::out_of_range'
  what():  vector::_M_range_check: __n (which is 18446744073709551615) >= this->size() (which is 1)
zsh: abort      sudo ASAN_OPTIONS=detect_leaks=0 ./src/bpftrace -e  aaa

Checklist

• Language changes are updated in docs/reference_guide.md
• User-visible and non-trivial changes updated in CHANGELOG.md
• The new behaviour is covered by tests