applets/devicenotifier: avoid duplicate entries in device list
Reason for the change
When a device is removed and added back immediately, the delay remove timer is still running, which means in m_devices the old device entry still exists. If the device is removed later, there is a chance that the associated ActionsControl is also deleted twice. To make sure that doesn't happen, always check if a timer is already running when a new device is added, if so, activate the timer to remove the old device.
Test plan
Screenshots or screen recordings
Bugs fixed
SENTRY: PLASMA-WORKSPACE-13P4