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
1 file changed