[instagram] improve error for non-existent profiles (#8550)

gallery_dl/extractor/instagram.py

@@ -871,8 +871,11 @@ class InstagramRestAPI():
     def user_by_name(self, screen_name):
         endpoint = "/v1/users/web_profile_info/"
         params = {"username": screen_name}
-        return self._call(
-            endpoint, params=params, notfound="user")["data"]["user"]
+        try:
+            return self._call(
+                endpoint, params=params, notfound="user")["data"]["user"]
+        except KeyError:
+            raise exception.NotFoundError("user")
 
     @memcache(keyarg=1)
     def user_by_id(self, user_id):