Fix move_camera method

[OSRS-B0b]

Issue: When calling move_camera and passing vertical=0 or horizontal=0 the camera will still move slightly in that direction

Steps to reproduce: run this code in an OSRSBot main_loop method

while True:
    time.sleep(1)
    self.move_camera(vertical=10)

Root cause: Even though the direction is passed as 0, move_camera still presses the key down and then up - it just sleeps for 0 seconds.

Solution: Don't call keypress when one direction = 0. (There is already logic that handles the case when both are 0.)