fix buffer overrun in eas_wtengine

avoid a buffer overrun in eas_wtengine.
Check buffer limits during application of gain
Clip calculated length in eas_wtsynth

Bug: 317780080
Test: POC with bug
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:6b66e7665dbcd891ff23081c13ab0b1637bb1dda)
backporting fix from main
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:f9d489385ecb04bbfe06f92d6fb03a69d2734fad)
Merged-In: I3609d6a36d89b26ae7eb3ae84cbe7772f6c3bee0
Change-Id: I3609d6a36d89b26ae7eb3ae84cbe7772f6c3bee0