follow_me_example: also check home position

Some versions of PX4 fail with this example because GPS checks are passed before a home position is set. The example code tries to arm without home position then, which is rejected.

Author: potaito

examples/follow_me_example.py

@@ -28,7 +28,7 @@ async def fly_drone():
 
     #Checking if Global Position Estimate is ok
     async for global_lock in drone.telemetry.health():
-        if global_lock.is_global_position_ok:
+        if global_lock.is_global_position_ok and global_lock.is_home_position_ok:
             print("-- Global position state is good enough for flying.")
             break