Fix FlipTDI crashing on Linux when connecting to a Linux system

[Jan200101]

What's new

• fixes crash in ftdi_usb_callback_tx_immediate due to assert

I'm not entirely sure how accurate my debugging was, the debugger kept pointing at furi_thread_get_id(ftdi_usb->thread) in the traceback and looking through the short furi_thread_get_id code shows that its checking the given pointer using furi_check and apparently thats where an assert was triggering.

I haven't managed to inspect the contents of ftdi_usb because it was optimized out and a log statement didn't print anything.

Verification

• Start FlipTDI
• Plug into Linux system
• verify the device is seen as an FT232H using dmesg
• exit app

Checklist (For Reviewer)

• PR has description of feature/bug or link to Confluence/Jira task
• Description contains actions to verify feature/bugfix
• I've built this code, uploaded it to the device and verified feature/bugfix