The built-in Wrap Paragraph command doesn't treat colons in any special way, and the only reason it would be breaking on one is if the word is longer than the line width. In that case, if it does break at the colon, it's just coincidence that it happened to become the last character on the line.
To change this, if you are applying the hack from this post, just add
wrapper.break_long_words = False
to the function as well. But I wouldn't really recommend that, as your edit will get wiped out any time Sublime gets updated.
The best solution is probably to use the Wrap Plus plugin.
It's default behaviour is ALSO to break on hyphens and long words, but it exposes a preference that lets you turn that off. Specifically, add
to your user preferences (or as a syntax-specific preference for LaTeX) to get the appropriate behaviour for LaTeX.