fixes error highlighting when selecting an error in another tab by joshgiesbrecht · Pull Request #1114 · processing/processing4

Fixes #1112

Current code finds start/end of highlight by finding char offsets based on the error's given line number; however, it's looking at the visible tab to do so, making the highlighting go wonky if you're selecting an error in a tab you don't have open yet.

Added one line to switch active tab before we find the char offsets.