What's broken:
bevel breaks when trying to bevel edges with a lonesome vertex between two n-gons.

• Worked in 2.77
• Broken since 2.78
• Tested on Windows & Linux

Steps to reproduce the bug:

1. Create any mesh
2. Use knife, cut zigzag inside a single face so that you get two n-gons after the cut
3. select cut edge and bevel