TypeError when parsing FFmpeg metadata due to string + float concatenation

[b2220765063]

moviepy crashes when parsing FFmpeg metadata if a field continuation attempts to concatenate a string and a float. This happens when _last_metadata_field_added refers to a value in metadata that is a float, and the parser assumes all metadata values are strings.

TypeError: can only concatenate str (not "float") to str
...
value = str(self._current_stream["metadata"][field]) + "\n" + value

This happens in FFmpegInfosParser.parse() when handling metadata field continuation lines where field == "".

Problematic Code (line 550 in video/io/ffmpeg_reader.py)

if field == "":
field = self._last_metadata_field_added
value = self._current_stream["metadata"][field] + "\n" + value

If self._current_stream["metadata"][field] is a float, this crashes.

Proposed Fix

if field == "":
field = self._last_metadata_field_added
value = str(self._current_stream["metadata"][field]) + "\n" + value

Environment
• OS: macOS
• Python: 3.12
• moviepy: 1.0.3
• ffmpeg: 6.1
• Video: .mov and .mp4 files with metadata fields like vendor_id, duration, etc.

This complements PR #2311, which fixed crashes due to colon-less metadata lines. However, this bug is still possible even after that patch, especially when the previous metadata field contains a float.