Avoid divide-by-zero in vp8 initialization

Check that the numerator is not zero. If it is, guess 30fps.

Fixes a clang IOC error in the quantize test. It's very unlikely for
this to occur in the wild because the setup in the quantize test is very
nonstandard.

Change-Id: Icdab7b81d4e168d3423e14db20787f960052e0c3
Fix the memory leak due to missing free frame_mvs.

Change-Id: I2ceee7341d906259002c0ea31ea009ae32c04bfd
Merge "Avoid divide-by-zero in vp8 initialization"
Merge "Fix the memory leak due to missing free frame_mvs."