Fix fuzzer-found undefined behavior in webrtc_cng
Fix fuzzer-found undefined behavior in webrtc_cng

The computation (x-127) << 8 is undefined for x < 127.
This CL replaces the shift with a multiplication: (x-127) * (1 << 8)

Bug: chromium:793201
Change-Id: I38b40bd88300208a0bfbbd8fe144b0a5b51a48ed
Reviewed-on: https://webrtc-review.googlesource.com/31800
Commit-Queue: Sam Zackrisson <b1a93beadfe1d2f7f0106ee02b6ffcdc950aa103@webrtc.org>
Reviewed-by: Henrik Lundin <b9599afb29b1fa4305dba8bb04f760bf0c9c9471@webrtc.org>
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#21205}
TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,TimothyGu/libilbc