Fix crash from out-of-bounds copy in WaveClipSpectrumCache::GetSpectrogram

Resolves: #8851

This fixes a crash bug in WaveClipSpectrumCache::GetSpectrogram. I've cleaned up the arithmetic for calculating the begin and end indices for copying cached spectrogram data. Previously copyBegin + oldX0 could exceed mSpecCache->len after shrinking mSpecCache, and this is where the crash on out of bounds access was coming from.

I've also renamed SpecCache::Grow to SpecCache::Resize to more accurately reflect what this function does, while also moving its invocation to after the crashing memmove to guarantee that we are never indexing out of bounds.

• I signed CLA
• The title of the pull request describes an issue it addresses
• If changes are extensive, then there is a sequence of easily reviewable commits
• Each commit's message describes its purpose and effects
• There are no behavior changes unnecessary for the stated purpose of the PR

Recommended:

• Each commit compiles and runs on my machine without known undesirable changes of behavior