Use .empty() instead of '!= ""'
Use .empty() instead of '!= ""'

R=b486136ee68458b09c92c86c39f451c87d6ef6a1@webrtc.org

Bug: None
Change-Id: I963d388de5be2eddf5094b0583178b2059fb4509
Reviewed-on: https://webrtc-review.googlesource.com/37940
Reviewed-by: Patrik Höglund <b486136ee68458b09c92c86c39f451c87d6ef6a1@webrtc.org>
Commit-Queue: Edward Lemur <d05609f027dc667cc37492b1dc1bdea5d60fa82a@webrtc.org>
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#21530}
ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,TimothyGu/libilbc