Add minor fixes to video_capture_ios.mm in order to make it more robust.
Add minor fixes to video_capture_ios.mm in order to make it more robust.

R=tkchin@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/46429005

Patch from Iurii Shevchuk <youwrk@gmail.com>.

Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#8763}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: da4fcc494ce29b6b504d88d7d6d8c129462288c6

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