Vim indentation broken with long match

[mahkoh]

Try gg=G-ing the following file:

https://gist.github.com/anonymous/87716d9ca0990d52cdff

It's very slow and breaks halfway down.

cc: @chris-morgan

[tomjakubowski]

Also slow and broken with a (pathologically) long function signature spread across many lines:

http://sprunge.us/higJ

[mahkoh]

Fixed #17212