Telescreen Updating Fix (#74424)

## About The Pull Request
Fixes https://github.com/tgstation/tgstation/issues/58843

Fixes the issue of only static being shown when closing the telescreen
while looking at a camera, then reopening the telescreen and selecting
the camera. Removes the static properly when reopening the telescreen,
instead of skipping it.
## Why It's Good For The Game

For most telescreens it wasn't too big of an issue, since it would just
mean reloading it by switching to a working camera, then back to the
desired camera. However, for telescreens connected to networks with only
one camera this isn't possible, meaning the telescreens become unusable
after closing it.
## Changelog
🆑
fix: fixes telescreens showing static when reopening a camera
/🆑

code/game/machinery/computer/camera.dm

@@ -169,6 +169,7 @@
 	// Turn off the console
 	if(length(concurrent_users) == 0 && is_living)
 		active_camera = null
+		last_camera_turf = null
 		playsound(src, 'sound/machines/terminal_off.ogg', 25, FALSE)
 		use_power(0)