Stuck at CONTENT_RESUME_REQUESTED preroll

I'm currently working on adding IMA SDK and noticed, then sometimes after playing content video fired CONTENT_RESUME_REQUESTED AdEvent, and then player stuck at buffering state.

Sample log, when playback is continued after preroll
```playbackState: 2
adEvent: LOADED
adEvent: CONTENT_PAUSE_REQUESTED
playbackState: 3
adEvent: STARTED
adError: No Ads VAST response after one or more Wrappers
adEvent: FIRST_QUARTILE
adError: No Ads VAST response after one or more Wrappers
adEvent: MIDPOINT
adEvent: THIRD_QUARTILE
playbackState: 2
adEvent: COMPLETED
adError: Linear assets were found in the VAST ad response, but none of them matched the video player's capabilities.
adEvent: ALL_ADS_COMPLETED
playbackState: 3 // PLAYING
```

And then sample log, when playback is stuck
```adError: No Ads VAST response after one or more Wrappers
adEvent: LOADED
adEvent: CONTENT_PAUSE_REQUESTED
playbackState: 3
adEvent: STARTED
adEvent: FIRST_QUARTILE
adError: Linear assets were found in the VAST ad response, but none of them matched the video player's capabilities.
adEvent: ALL_ADS_COMPLETED
adEvent: MIDPOINT
adEvent: THIRD_QUARTILE
adEvent: COMPLETED
adEvent: CONTENT_RESUME_REQUESTED
adEvent: ALL_ADS_COMPLETED
playbackState: 2 // BUFFERING
```

Sometimes I get AdErrorCode [name: VAST_LINEAR_ASSET_MISMATCH, number: 403], but it does not affects playback and keeps loading as usual.

That's my first encounter with IMA SDK, so I can't say, was this problem before. My Exoplayer version currently is latest (2.14.2)

Again, player stuck only when CONTENT RESUME REQUESTED event firing. Same problem I found via #6728 so I decided to reopen issue since I found regression, since the code has undergone many changes since then and I couldn't found any workaround

Thank you!