MP 1.3.64 won't start on linux

#### Issue details
mono MissionPlanner.exe won't start on linux.

#### Version
1.3.64, I also tried 1.3.62, same thing.

#### Logs
MONO_LOG_LEVEL=debug mono MissionPlanner.exe > mono_mp.log
gives this when I start MP, the splash screen opens, I count to about 10 seconds, and then press ctrl-c on the terminal that started it:
see attached log.
[mono_mp.log](https://github.com/ArduPilot/MissionPlanner/files/3050371/mono_mp.log)

Start with the reported MissionPlanner.exe launch command on Linux and inspect the attached mono_mp.log, including the MONO_LOG_LEVEL=debug output. Reproduce with Mission Planner 1.3.64 or 1.3.62 under Mono, then identify the startup failure; done means the application reaches a usable window without requiring Ctrl-C.

Written by the indexing model from the issue text.