lister/core: Fix missing use case about no response from api server

UnboundLocalError could happen otherwise

swh/lister/core/indexing_lister.py

@@ -174,6 +174,9 @@ class SWHIndexingLister(SWHListerBase):
             logging.info('listing repos starting at %s' % index)
 
             response, injected_repos = self.ingest_data(index)
+            if not response and not injected_repos:
+                logging.info('No response from api server, stopping')
+                break
 
             next_index = self.get_next_target_from_response(response)
 

swh/lister/core/lister_base.py

@@ -285,6 +285,7 @@ class SWHListerBase(abc.ABC, config.SWHConfig):
         """
         retries_left = self.MAX_RETRIES
         do_cache = self.config['cache_responses']
+        r = None
         while retries_left > 0:
             try:
                 r = self.transport_request(identifier)
@@ -486,6 +487,8 @@ class SWHListerBase(abc.ABC, config.SWHConfig):
         """
         # Request (partial?) list of repositories info
         response = self.safely_issue_request(identifier)
+        if not response:
+            return response, []
         models_list = self.transport_response_simplified(response)
         models_list = self.filter_before_inject(models_list)
         if checks:

swh/lister/core/page_by_page_lister.py

@@ -121,7 +121,10 @@ class PageByPageLister(SWHListerBase):
 
             response, injected_repos = self.ingest_data(page,
                                                         checks=check_existence)
-            if not injected_repos:
+            if not response and not injected_repos:
+                logging.info('No response from api server, stopping')
+                break
+            elif not injected_repos:
                 logging.info('Repositories already seen, stopping')
                 break