audiopolicy: fix wrong volume db value for voice call stream

When apply mute for voice stream, vol index 0 is set, while
voice stream minimum vol index is 1. This will cause negative
vol index is calculated and maximum db value is set.

Ensure vol index is valide to calculate.

Also add range check in rescaleVolumeIndex().

Bug: 123063166
Test: make
CRs-Fixed: 2056642
Change-Id: I89ee64d0914a971194a72b4de483d88b5029d80e