[export] Also check the id field of a CCS problem to see if it already exists

In DOMjudge 8.4, entities will always be identified by a string rather than an auto-incrementing number.

Author: mpsijm

bin/export.py

@@ -527,7 +527,7 @@ def get_problems():
     def get_problem_id(problem):
         nonlocal ccs_problems
         for p in ccs_problems:
-            if p['short_name'] == problem.name or p.get('externalid') == problem.name:
+            if problem.name in [p.get('short_name'), p.get('id'), p.get('externalid')]:
                 return p['id']
 
     for problem in problems: