VTOL Tailsitter: treat back transition abort like a front transition

for throttle blending.

Signed-off-by: Silvan Fuhrer <silvan@auterion.com>

src/modules/vtol_att_control/tailsitter.cpp

@@ -121,6 +121,7 @@ void Tailsitter::update_vtol_state()
 		case vtol_mode::TRANSITION_BACK:
 			// failsafe into fixed wing mode
 			_vtol_mode = vtol_mode::FW_MODE;
+			_trans_finished_ts = hrt_absolute_time();
 			break;
 		}
 	}