termux-microphone-record: cannot record into fifo or block device files

Problem description
termux-microphone-record isn't capable of writing to nonstandard files. This is caused by MicRecorderAPI.java:254 checking if the target file exists, which for fifos and block devices under current file handling, it does.

Steps to reproduce

mkfifo myFifo
termux-microphone-record -f myFifo # File: myFifo already exists! Please specify a different filename

termux-microphone-record -f /dev/stdout # File: stdout already exists! Please specify a different filename

Expected behavior
The module should be able to write to fifo/block device files.
This would also allow directly processing output using other applications, as well as streaming over the network.

Additional information

• termux-api application version: 0.50.1
• termux-api package version (installed through apt): 0.57
• Android OS version: 11 (lineage_twolip-userdebug 11 RQ3A.211001.001 1003680)
• Device model: Redmi Note 6 Pro

Start at MicRecorderAPI.java:254 and reproduce the issue with a FIFO or /dev/stdout using termux-microphone-record. Trace the existing-target check and verify that recording can write to FIFO and block-device paths while preserving the different-filename error for regular files.