Check issue key when downloading (#56)

diff --git a/migration/src/download_jira.py b/migration/src/download_jira.py
index 9fb5c04..13c8f8c 100644
--- a/migration/src/download_jira.py
+++ b/migration/src/download_jira.py
@@ -41,9 +41,16 @@
     if res.status_code != 200:
         logger.warning(f"Can't download {issue_id}. status code={res.status_code}, message={res.text}")
         return False
+    data = res.json()
+    if "key" not in data:
+        logger.warning(f"The issue's key does not exist. Skipped {issue_id}")
+        return False
+    if data["key"] != issue_id:
+        logger.warning(f"The issue key {data['key']} does not match the request key {issue_id}. Maybe this was moved.")
+        return False
     dump_file = jira_dump_file(dump_dir, num)
     with open(dump_file, "w") as fp:
-        json.dump(res.json(), fp, indent=2)
+        json.dump(data, fp, indent=2)
     logger.debug(f"Jira issue {issue_id} was downloaded in {dump_file}.")
     return True