Laser altimeter over water causes RTL

#### Issue details
When using a laser altimeter and the "Terrain" option in mission planner, We have found that if the drone transits over water (pond) the drone will enter RTL.
This is due to the reduced range of the Laser Alt over water, it appears to see the loss of laser range as a terrain error (RTL)

Is there a way or addition that can be made to effectively continue mission in the event of? Using Baro only?
Thanks in advance
Laser Alt used SF11c

#### Version
3.4.6

#### Platform
Copter
#### Airframe type
Hex

#### Hardware type
Pixhawk2.4.8

No source file or test is named. Start by reproducing the Terrain mission behavior with the SF11c laser altimeter over water and trace how loss of laser range leads to RTL. Done means the intended behavior for unavailable laser terrain data is defined and verified without an unsafe RTL.

Written by the indexing model from the issue text.