remove useless search in users query

appservice/db.py

@@ -113,11 +113,8 @@ class DataBase:
         """
 
         with self.lock:
-            self.cur.execute("SELECT * FROM users")
+            self.cur.execute("SELECT * FROM users where mxid = ?", [mxid])
-            users = self.cur.fetchall()
 
-        user: dict = next(
+            user = self.cur.fetchone()
-            iter([user for user in users if user["mxid"] == mxid]), {}
-        )
 
-        return user
+        return {} if not user else user