fix(old-safari): check RTCRtpTransceiver exists before checking prototype

modules/browser/BrowserCapabilities.js

             return true;
         }
 
-        if (this.isSafariWithVP8()) {
+        if (this.isSafariWithVP8() && typeof window.RTCRtpTransceiver !== 'undefined') {
             // eslint-disable-next-line max-len
             // https://trac.webkit.org/changeset/236144/webkit/trunk/LayoutTests/webrtc/video-addLegacyTransceiver.html
             // eslint-disable-next-line no-undef