show send errors in UI

src/domain/session/room/RoomViewModel.js

@@ -66,7 +66,16 @@ export default class RoomViewModel extends EventEmitter {
 
     sendMessage(message) {
         if (message) {
+            try {
                 this._room.sendEvent("m.room.message", {msgtype: "m.text", body: message});
+            } catch (err) {
+                console.error(`room.sendMessage(): ${err.message}:\n${err.stack}`);
+                this._timelineError = err;
+                this.emit("change", "error");
+                return false;
             }
+            return true;
+        }
+        return false;
     }
 }

src/ui/web/session/room/MessageComposer.js

@@ -16,8 +16,9 @@ export default class MessageComposer extends TemplateView {
 
     _onKeyDown(event) {
         if (event.key === "Enter") {
-            this.viewModel.sendMessage(this._input.value);
+            if (this.viewModel.sendMessage(this._input.value)) {
                 this._input.value = "";
             }
         }
+    }
 }