When I select previous firmware higher than 3.5.7 for Quad X, MP displays 3.5.7 only.

#### Issue details
I tryed to roll back from 3.6.5 to 3.6.4 and select 3.6.4 as previous firmware.
But Mission Planner displays 3.5.7 on Quad X flash button.
If I select firmware lower than 3.5.7, no problem.

Image1 : When I select lower than 3.5.7, Mission Planner displays correct version number.

Image2 : When I select higher than 3.5.7, Mission Planner displays incorrect version number(3.5.7).

Image3 : When I select higher than 3.5.7, confirm dialog displays incorrect version number too.

Image4 : If I click "OK" button on confirm dialog(Image3), Mission Planner flashes 3.6.4(correct).

So this issue is just display issue on Mission Planner.

#### Version
Mission Planner 1.3.62 build 1.3.6967.4622
I clicked "Check for BETA Updates" button at HELP menu.

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

#### Airframe type
Copter Quad X

#### Hardware type
Pixhawk 2.4.8

#### Logs
No logs.

Reproduce the rollback flow in Mission Planner 1.3.62 with a Quad X by selecting firmware above and below 3.5.7, then trace the UI code that supplies the version shown on the flash button and confirmation dialog. Done means both displays show the selected version, while the existing flash action continues to use the correct firmware.

Written by the indexing model from the issue text.