Replace c-style cast and constrain value in VCMFecMethod::ProtectionFactor.

BUG=None

Review-Url: https://codereview.webrtc.org/2501083003
Cr-Original-Commit-Position: refs/heads/master@{#15116}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 05f845d025a8289851d7080501d1ff08e478e7f1
1 file changed