Fallback to default aspect ratio if not provided

This is to fix the regression introduced by ag/26340832. When apps like
YT provide empty aspect ratio via PictureInPictureParams, the zero value
would be used to calculate the min / max allowed size and causes the PiP
window to be resized unexpectedly.

Video: http://recall/-/aaaaaabFQoRHlzixHdtY/frCUwuTnpvVPMqFs3C5Gnk
Bug: 328051931
Test: manual, follow the reproduce steps, see video
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:63c0f02a731151d7b5ec6ea3a1a1466f0774cc32)
Merged-In: Icab07e634cbd3c19668640203b586f10219c0410
Change-Id: Icab07e634cbd3c19668640203b586f10219c0410