Unmatched parentheses in i18n check break the regex

[Otto42]

Reported here:
https://wordpress.org/support/topic/bug-i-guess?replies=2#post-6175594

Example:
_e( 'text field (you can leave it blank', 'mytheme' );

Likely solution: tokenize the whole file instead of just that line. Similar to the patch for this:
#1

[Otto42]

Given the speed problems this already has, no. Let it break. Maybe detect it and fail themes that are doing it, but strings in translation need to be complete, not partial. Wontfix.