Display fixed location and satellites graph after F9P disconnection

[pyrog]

To Reproduce
Steps to reproduce the behavior:

1. Go to http://basegnss.local/status
2. Power off the F9P board
3. The status page continue to display the same graph and coordinates
4. Power on the F9P
5. The status page continue to display the same graph and coordinates
6. Go to http://basegnss.local/settings
7. Start the main service: the button is yellow
8. Press the View diagnostic button

Expected behavior
A clear and concise description of what you expected to happen.

Software/Hardware (please complete the following information):

• RTKBase release number 2.3.0
• OS: Raspberry Pi Os
• SBC: Raspberry Pi 3B+
• GNSS Device: Ublox F9P
• Connection type: usb

Screenshots

Additional context
str2str_tcp.service : Active
● str2str_tcp.service - RTKBase Tcp
Loaded: loaded (/etc/systemd/system/str2str_tcp.service; disabled; vendor preset: enabled)
Active: activating (auto-restart) (Result: exit-code) since Mon 2021-07-12 08:23:48 CEST; 29s ago
Process: 3259 ExecStart=/home/basegnss/rtkbase/run_cast.sh in_serial out_tcp (code=exited, status=0/SUCCESS)
Main PID: 3266 (code=exited, status=255/EXCEPTION)
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