Transmission archive fix

[taclane]

Beginning with trunk-recorder 4.6, transmission .wav files exist in a temporary directory and either get deleted, or moved to the captureDir structure if transmissionArchive is set in the config file.

Related to PR #796, trunk-recorder may crash if it attempts file operations on a non-existent transmission .wav in the tempDir.

This fix simply uses the existing checkIfFile() to verify if the file exists before attempting to move a transmission .wav from the captureDir.

[taclane]

Below is the error leading to this crash that was investigated on the t-r discord.

[2023-07-10 12:17:52.011707] (error)   Somehow, /dev/shm/trs/4409-1689005860_776568750.wav doesn't exist, not attempting to provide it to sox
terminate reached from thread id: 7fe5fbf81dc0Got std::runtime_error
boost::filesystem::copy_file: No such file or directory: "/dev/shm/trs/4409-1689005860_776568750.wav", "/app/trs/2023/7/10/4409-1689005860_776568750.wav"
0x7fe60062e5d9: (gr::tagged_stream_block::check_topology(int, int)+0x2e49)
0x7fe60022b24c: (std::rethrow_exception(std::__exception_ptr::exception_ptr)+0x7c)
0x7fe60022b2b7: (std::terminate()+0x17)
0x7fe60022b23e: (std::rethrow_exception(std::__exception_ptr::exception_ptr)+0x6e)
0x562a6d78a60c: (Call_Concluder::manage_call_data_workers()+0xe2c)
0x562a6d6ac5e4: (monitor_messages()+0x394)
0x562a6d6a01f0: (main+0x740)
0x7fe5ffe77d90: (__libc_init_first+0x90)
0x7fe5ffe77e40: (__libc_start_main+0x80)
0x562a6d6a3a95: (_start+0x25)
Aborted (core dumped)

[robotastic]

Nice Catch!