If we `set pastetoggle=abcde`, and manually type it, then `vgetorpeek()`
sees part of the option before it has all been inserted into the
typebuffer.
To signify this it sets `keylen = KEYLEN_PART_KEY`, but the condition
about whether to return the current key from `vgetorpeek()` only checks
for `keylen = KEYLEN_PART_MAP`.
Add a check for `KEYLEN_PART_KEY` to account for the `'pastetoggle'`
option.