[PATCH 0/1] MR11143: mfplat/tests: Avoid crash if mediasource retrieval failed.

[Bernhard Übelacker (＠bernhardu)]

Followup to e438931e48.

[Test pattern page mfplat:mfplat](https://test.winehq.org/data/patterns.html#mfplat:mfplat)

[Testbot run with this patch](https://testbot.winehq.org/JobDetails.pl?Key=163375)

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https://gitlab.winehq.org/wine/wine/-/merge_requests/11143