fix: handle 0 item response in querysets

A flaw in the __iter__ logic introduced to handle scenarios
where a pagination element is not included in the response xml
resulted in an infinite loop. This PR introduces a few changes
to protect against this:

1. After running QuerySet._fetch_all(), if the result_cache is
empty, return instead of performing other comparisons.
2. Ensure that any non-None total_available is returned from
the PaginationItem's object.
3. In _fetch_all, check if there is a PaginationItem that has been
populated so as to not call the server side endpoint muliple times
before returning.

tableauserverclient/server/query.py

@@ -85,6 +85,8 @@ def __iter__(self: Self) -> Iterator[T]:
                     # up overrunning the total number of pages. Catch the
                     # error and break out of the loop.
                     raise StopIteration
+            if len(self._result_cache) == 0:
+                return
             yield from self._result_cache
             # If the length of the QuerySet is unknown, continue fetching until
             # the result cache is empty.
@@ -150,7 +152,7 @@ def _fetch_all(self: Self) -> None:
         """
         Retrieve the data and store result and pagination item in cache
         """
-        if not self._result_cache:
+        if not self._result_cache and self._pagination_item._page_number is None:
             response = self.model.get(self.request_options)
             if isinstance(response, tuple):
                 self._result_cache, self._pagination_item = response
@@ -159,7 +161,7 @@ def _fetch_all(self: Self) -> None:
                 self._pagination_item = PaginationItem()
 
     def __len__(self: Self) -> int:
-        return self.total_available or sys.maxsize
+        return sys.maxsize if self.total_available is None else self.total_available
 
     @property
     def total_available(self: Self) -> int:

test/test_pager.py

@@ -1,6 +1,7 @@
 import contextlib
 import os
 import unittest
+import xml.etree.ElementTree as ET
 
 import requests_mock
 
@@ -122,3 +123,14 @@ def test_pager_view(self) -> None:
             m.get(self.server.views.baseurl, text=view_xml)
             for view in TSC.Pager(self.server.views):
                 assert view.name is not None
+
+    def test_queryset_no_matches(self) -> None:
+        elem = ET.Element("tsResponse", xmlns="http://tableau.com/api")
+        ET.SubElement(elem, "pagination", totalAvailable="0")
+        ET.SubElement(elem, "groups")
+        xml = ET.tostring(elem).decode("utf-8")
+        with requests_mock.mock() as m:
+            m.get(self.server.groups.baseurl, text=xml)
+            all_groups = self.server.groups.all()
+            groups = list(all_groups)
+        assert len(groups) == 0