stops processing multiple files on pysubs2.exceptions.UnknownFPSError

multiple bugs here

expected:

• show a warning, continue to process other subtitle files
• print filename of the problematic subtitle file
• in *.sub files, parse FPS from {1}{1}25.0 etc (not from first line)

$ ffs --version
ffsubsync 0.4.22

$ ffs --overwrite-input movie.mp4 -i *.srt *.sub
...
Traceback (most recent call last):
  File "/lib/python3.10/site-packages/pysubs2/microdvd.py", line 38, in from_file
    fps = float(text)
ValueError: could not convert string to float: 'Advertise your product or brand here|contact www.OpenSubtitles.org today\r'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
...
  File "/lib/python3.10/site-packages/pysubs2/microdvd.py", line 42, in from_file
    raise UnknownFPSError("Framerate was not specified and "
pysubs2.exceptions.UnknownFPSError: Framerate was not specified and cannot be read from the MicroDVD file.

problematic subtitle file

$ head -n3 "The.Unbearable.Lightness.Of.Being.1988.en.156226.sub"
{25}{175}Advertise your product or brand here|contact www.OpenSubtitles.org today
{496}{567}[Bell Tolling]
{568}{642}[Pigeons Cooing]

Start with the ffs command path that processes multiple subtitle inputs and the pysubs2/microdvd.py traceback shown in the issue. Reproduce with the provided *.srt and *.sub command and the sample MicroDVD file. Done means an invalid subtitle produces a warning with its filename, other files continue processing, and FPS is read from a valid frame line such as {1}{1}25.0.