updateSessionTimestamp: return false if no write to DB needed

ts/session/protocols/SessionProtocol.ts

@@ -220,17 +220,15 @@ export class SessionProtocol {
     timestamp: number | undefined,
     map: StringToNumberMap
   ): Promise<boolean> {
+    if (map[device] === timestamp) {
+      return false;
+    }
     if (!timestamp) {
-      if (device in map) {
       // tslint:disable-next-line: no-dynamic-delete
       delete map[device];
-
+    } else {
-        return true;
-      }
-
-      return false;
-    }
       map[device] = timestamp;
+    }
 
     return true;
   }