Fix openstenoproject#1585

Unplugging and then plugging in a USB device causes the operating system to reset the keymap. To avoid Plover sending key presses for keys it had previously configured but which are not mapped after the reset it is necessary to reset the keyboard emulator when resetting the machine after reconnecting so that Plover assumes the default keymap and any unmapped symbols will be added again

plover/engine.py

@@ -241,6 +241,8 @@ def _update(self, config_update=None, full=False, reset_machine=False):
             self._machine_params = machine_params
             update_keymap = True
             start_machine = True
+            # initialize keyboard emulation again to force update of keymap
+            self._keyboard_emulation.__init__()
         elif self._machine is not None:
             update_keymap = 'system_keymap' in config_update
         if update_keymap: