[Fix] fix restoration_video_demo bug

[Z-Fran]

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Motivation

Fix restoration_video_demo bug of some input directory cases.

Modification

mmedit/apis/restoration_video_inference.py

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BC-breaking (Optional)

Does the modification introduce changes that break the backward-compatibility of the downstream repositories?
If so, please describe how it breaks the compatibility and how the downstream projects should modify their code to keep compatibility with this PR.

Use cases (Optional)

If this PR introduces a new feature, it is better to list some use cases here, and update the documentation.

Checklist

Before PR:

• I have read and followed the workflow indicated in the CONTRIBUTING.md to create this PR.
• Pre-commit or linting tools indicated in CONTRIBUTING.md are used to fix the potential lint issues.
• Bug fixes are covered by unit tests, the case that causes the bug should be added in the unit tests.
• New functionalities are covered by complete unit tests. If not, please add more unit test to ensure the correctness.
• The documentation has been modified accordingly, including docstring or example tutorials.

After PR:

• If the modification has potential influence on downstream or other related projects, this PR should be tested with some of those projects.
• CLA has been signed and all committers have signed the CLA in this PR.

[codecov]

Codecov Report

Base: 83.86% // Head: 83.87% // Increases project coverage by +0.00% 🎉

Coverage data is based on head (a2a2cfc) compared to base (bef5816).
Patch coverage: 0.00% of modified lines in pull request are covered.

❗ Current head a2a2cfc differs from pull request most recent head e937b60. Consider uploading reports for the commit e937b60 to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1262   +/-   ##
=======================================
  Coverage   83.86%   83.87%           
=======================================
  Files         223      223           
  Lines       12739    12736    -3     
  Branches     1990     1990           
=======================================
- Hits        10684    10682    -2     
+ Misses       1716     1715    -1     
  Partials      339      339           

Flag	Coverage Δ
unittests	83.87% <0.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
mmedit/apis/restoration_video_inference.py	16.36% <0.00%> (-2.61%)	⬇️

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[zengyh1900]

The modifications look good to me. Please merge it after it passes all the checks.