Loading saved Rally Points

#### Issue details
In Plan, select Rally. Left click map to add Rally point. Writing this RP to the FC board is fine.

'Save File' then 'Load File'

The loaded file includes an extra line 'unknown'
Writing the RP to the FC board fails. Deleting the extra line 'unknow' allows the loaded file to be written to the FC board.

#### Version
Latest beta MP, Arduplane 4.2.0dev

#### Platform
[ ] All
[ ] AntennaTracker
[ ] Copter
[ x ] Plane
[ ] Rover
[ ] Sub

#### Airframe type
Plane

#### Hardware type
SITL (but assume the same issue exists with an actual board)

#### Logs
_Please provide a link to any relevant logs that show the issue_

Start by reproducing the issue in Plan > Rally with SITL: save a rally point, load the file, and compare the loaded content with the saved content. Done means the loaded rally point can be written to the FC board without manually removing the extra "unknown" line.

Written by the indexing model from the issue text.