Adds additional check, avoids undefined error.
Adds additional check, avoids undefined error.

Needs an additional check for available devices after merging https://github.com/jitsi/lib-jitsi-meet/pull/139.

jitsi/lib-jitsi-meet,adambowles/lib-jitsi-meet,jiyeyuran/lib-jitsi-meet,nevermind-corp/ljm,dmurtari/lib-jitsi-meet,damencho/lib-jitsi-meet,jitsi/lib-jitsi-meet,adambowles/lib-jitsi-meet,dmurtari/lib-jitsi-meet