navigator: bugfix to prevent NaN setpoints

The asinf function is NaN outside of -1 to 1. Therefore, it probably
makes sense to constrain the input to prevent NaN setpoints further down
the line.

src/modules/navigator/mission_block.cpp

@@ -387,7 +387,9 @@ MissionBlock::is_mission_item_reached()
 			     _mission_item.nav_cmd == NAV_CMD_LOITER_TO_ALT)) {
 
 				float bearing = get_bearing_to_next_waypoint(curr_sp.lat, curr_sp.lon, next_sp.lat, next_sp.lon);
-				float inner_angle = M_PI_2_F - asinf(_mission_item.loiter_radius / range);
+				// We should not use asinf outside of [-1..1].
+				const float ratio = math::constrain(_mission_item.loiter_radius / range, -1.0f, 1.0f);
+				float inner_angle = M_PI_2_F - asinf(ratio);
 
 				// Compute "ideal" tangent origin
 				if (curr_sp.loiter_direction > 0) {