Make sanitizeMediaMetadata optimization more robust

Even if the MediaMetadata contains URIs, but they don't require sanitization,
avoid making a copy of the MediaMetadata.
This is a follow-up to ag/32909078 that makes the optimization apply in
additional use cases.

Flag: EXEMPT bugfix
Bug: 407234313
Bug: 271851153
Change-Id: I79ea867d8ad84109ed4483bd413ea32cf1aecd8a