monobit uses "." in directory name as an extension

[hackerb9]

$ mkdir -p a.b/c/

$ monobit-convert crt8002/crt8002-005.yaff a.b/foo.png
ERROR: Overwriting existing file 'home/rob/hoard-of-bitfonts/a.b' requires -overwrite to be set

$ monobit-convert crt8002/crt8002-005.yaff a.b/c/foo.png
[Succeeds]

$ monobit-convert crt8002/crt8002-005.yaff no.such.dir/foo.png
ERROR: Cannot open subpath 'foo.png' on non-container stream <Stream name='home/rob/hoard-of-bitfonts/no.such.dir' mode='w'>'

$ ls -l no.such.dir
-rw-rw-r-- 1 rob rob 0 Jan 27 12:34 no.such.dir

Monobit should not be looking at the directory name for the file extension.

Notes: Periods are okay in any part of the path except the immediate containing directory. Specifying a non-existent directory creates it, but as a file not a directory.