backward/forward-[kill-]bigword movement incorrect with single-char words

[lilyball]

When using the bigword movement or kill bindings (forward-bigword, backword-bigword, etc) the movement is incorrect when the bigword is only one character long. In particular, forward-bigword acts like I'd expect forward-char forward-bigword to act, and similarly for backward. This also affects the kill variant.

For example, given the following, where | is the current character position:

echo a b c d|

Executing backward-bigword produces

echo a b |c d

instead of the expected

echo a b c |d

fish 3.1.2