multiaircraft logfiles are put into wrong folder/s by first-seen-sysid, or something semi-random

#### Issue details
when MissionPlanner is connected to multiple aircraft, and gets packet/s for multiple different sysids, the behaviour that defines which folder the logfile/s are created appears to be pseudo-random.

#### Version
all
#### Platform
[ ] All
[ ] AntennaTracker
[ ] Copter
[ X ] Plane
[ ] Rover
[ ] Sub

#### Airframe type
not relevant
#### Hardware type
pixhawk, but any should be similar

#### Logs
look in User/Documents/Mission Planner/logs/FIXED_WING, and you'll see folder/s for each aircraft sysid, except for multi-vehicle ops with multiple sysids at once, it's not as you'd expect here. you have to search all the subfolder/s for a logfile as it could be under any of the sysid/s that you were using at that time.

Reproduce the issue in Mission Planner with multiple aircraft and sysids, then inspect how logfiles are placed under User/Documents/Mission Planner/logs/FIXED_WING. Confirm that each logfile is consistently stored in the folder for the aircraft sysid that produced it, including simultaneous multi-vehicle operations.

Written by the indexing model from the issue text.