On GetCapabilities() failure, caps.cDestinations is left uninitialized.
Without a protection the following code runs in a random loop
in the worst case up to 0xFFFFFFFF times.
for (destId = 0; destId < caps.cDestinations; destId++)
{
GetDestinationLineInfo(mixId, destId, destLine);
BUG=webrtc:4882
Review URL: https://codereview.webrtc.org/1269563002
Cr-Commit-Position: refs/heads/master@{#9663}
a12ba5502c