joy2key: fix spurious initialization events

For certain joysticks (axis), SDL will generate spurious axis movement events during initialization.
It seems that for axis where `absmin` and `absmax` are asymmetrical (ex. 0-255 instead of -255 - 255), SDL generates extra events which are not user generated. This can causes issues - i.e. automatically trigger the `runcommand` menu without user interaction, unintended scrolling, etc.

As a workaround, discard any axis movement events _immediately_ after the device is added.
NOTE: this will discard any potential valid axis events from another (already connected) device if they are present, forcing the user to probably re-center the joystick they were using.

Author: cmitu

scriptmodules/admin/joy2key/joy2key_sdl.py

@@ -38,7 +38,7 @@
 from sdl2 import joystick, events, version, \
     SDL_WasInit, SDL_Init, SDL_QuitSubSystem, SDL_GetError, \
     SDL_INIT_JOYSTICK, SDL_INIT_VIDEO, version_info, \
-    SDL_Event, SDL_PollEvent, SDL_Delay, SDL_Quit, \
+    SDL_Event, SDL_PollEvent, SDL_FlushEvent, SDL_Delay, SDL_Quit, \
     SDL_JOYDEVICEADDED, SDL_JOYDEVICEREMOVED, SDL_QUIT, \
     SDL_JOYBUTTONDOWN, SDL_JOYBUTTONUP, SDL_JOYHATMOTION, SDL_JOYAXISMOTION, \
     SDL_GetTicks
@@ -352,6 +352,8 @@ def handle_new_input(e: SDL_Event, axis_norm_value: int = 0) -> bool:
                 if joystick.SDL_JoystickNumAxes(stick) > 0:
                     axis_prev_values[joystick.SDL_JoystickInstanceID(stick)] = [0 for x in range(joystick.SDL_JoystickNumAxes(stick))]
 
+                # Remove any spurious axis movements reported by SDL during initialization
+                SDL_FlushEvent(SDL_JOYAXISMOTION);
                 continue
 
             if event.jdevice.which not in active_devices: