Hope this will make people using feed_command less likely: this hides bugs.
Already found at least two:
1. msgpackparse() will show internal error: hash_add() in case of duplicate
keys, though it will still work correctly. Currently silenced.
2. ttimeoutlen was spelled incorrectly, resulting in option not being set when
expected. Test was still functioning somehow though. Currently fixed.
Closes#5449
A file containing the string "vim" followed by a very large number in a modeline
location will trigger an overflow in getdigits() which is called by
chk_modeline() when trying to parse the version number.
Add getdigits_safe(), which does not assert overflows, but reports them to the
caller.
