Fix: Allow exporting of videos with unknown duration (e.g. streaming WebM)

[Sandeep6135]

Description

This pull request fixes a critical bug where videos missing duration metadata (such as streaming WebM blobs where video.duration is Infinity) were completely blocked from being exported.

The Problem:
When extractMetadata encountered a video with Infinity duration, it correctly fell back to setting the duration to 0. However, the validation checks in useVideoEditor.ts rigidly enforced that trimStart (default 0) must be earlier than the duration. This caused 0 >= 0 to evaluate to true, instantly failing the validation and throwing a "Trim start time must be earlier than the end time" error, making these videos completely unexportable.

The Solution:
Updated the validation logic in useVideoEditor.ts to smartly bypass the duration constraint when duration === 0 (meaning it's unknown/missing metadata).

• If the user sets a custom trimEnd, we still rigidly enforce trimStart < trimEnd.
• If trimEnd is null and duration is missing, we safely allow the export to proceed to FFmpeg without failing the pre-flight checks.

Testing:

• Verified that standard videos with valid durations still validate correctly.
• Verified that videos with missing duration metadata (duration 0) no longer fail the initial export checks and proceed properly to the engine.

Closes #955.

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Project	Deployment	Actions	Updated (UTC)
reframe	Ready	Preview, Comment	May 23, 2026 11:04am

[Sandeep6135]

@magic-peach I have starred the repo already.
However I can notice that you haven't added GSSoC labels(eg. gssoc:approved, gssoc, etc.) to this PR.
Kindly add them as they are evaluated and you know that better than anyone else in here.
Thank you!