unlink: mainspace pages with colon are parsed incorrectly

[NovemLinguae]

Example: https://test.wikipedia.org/wiki/Cyber_Seduction:_His_Secret_Life

Running TW->Unlink on this page will not work because it has a colon in the title. It will throw this error.

Reported by Liz at WT:TWINKLE - https://en.wikipedia.org/wiki/Wikipedia_talk:Twinkle#Problem_with_unlinking_backlinks

Line of code where error is occurring:

twinkle/morebits.js

Lines 4929 to 4932 in 10021f1

	var idx = link_target.indexOf(':');
	if (idx > 0) {
	ns = link_target.slice(0, idx);
	title = link_target.slice(idx + 1);