fix(participant): update local name only on explicit update (#3849)

Dominant speaker events can trigger local participant updates
without a display name. Do not update the name unless there
is an explicit update in the action.

react/features/base/conference/middleware.js

     const { participant } = action;
     const result = next(action);
 
-    if (conference && participant.local) {
+    if (conference && participant.local && 'name' in participant) {
         conference.setDisplayName(participant.name);
     }