messages: Update metadata handling for message reaction.

This commit is in sync with the new metadata changes for
reactions data sent in messages API. It uses user_id
for identification of the reaction's user.

tests/ui_tools/test_messages.py

@@ -1597,6 +1597,22 @@ def test_transform_content(self, mocker, raw_html, expected_content):
     @pytest.mark.parametrize(
         "to_vary_in_each_message, expected_text, expected_attributes",
         [
+            case(
+                {
+                    "reactions": [
+                        {
+                            "emoji_name": "thumbs_up",
+                            "emoji_code": "1f44d",
+                            "user_id": 1001,
+                            "reaction_type": "unicode_emoji",
+                        },
+                    ],
+                },
+                "  :thumbs_up: 1  ",
+                [
+                    ("reaction", 17),
+                ],
+            ),
             case(
                 {
                     "reactions": [

zulipterminal/ui_tools/messages.py

@@ -272,10 +272,16 @@ def reactions_view(
             my_user_id = self.model.user_id
             reaction_stats = defaultdict(list)
             for reaction in reactions:
-                user_id = int(reaction["user"].get("id", -1))
+                user_id = reaction.get("user_id", -1)
                 if user_id == -1:
-                    user_id = int(reaction["user"]["user_id"])
-                user_name = reaction["user"]["full_name"]
+                    user_id = int(reaction["user"].get("id", -1))
+                    if user_id == -1:
+                        user_id = int(reaction["user"]["user_id"])
+                if user_id is None:
+                    user_name = reaction["user"]["full_name"]
+                user = self.model.get_user_info(user_id)
+                if user is not None:
+                    user_name = user.get("full_name", None)
                 if user_id == my_user_id:
                     user_name = "You"
                 reaction_stats[reaction["emoji_name"]].append((user_id, user_name))