gh-156067: Fix two error handling issues in _zoneinfo.load_data() (GH-156068)

(cherry picked from commit 21a6a8a)

Co-authored-by: Stan Ulbrych <stan@python.org>

Author: StanFromIreland

Misc/NEWS.d/next/Library/2026-08-19-21-01-19.gh-issue-156067.1CXkqc.rst

@@ -0,0 +1,2 @@
+Fix error handling in the :mod:`zoneinfo` accelerator module when a
+transition index is ``-1`` or a TZ string's ``__bool__`` raises.

Modules/_zoneinfo.c

@@ -1067,7 +1067,7 @@ load_data(zoneinfo_state *state, PyZoneInfo_ZoneInfo *self, PyObject *file_obj)
         }
 
         Py_ssize_t cur_trans_idx = PyLong_AsSsize_t(num);
-        if (cur_trans_idx == -1) {
+        if (cur_trans_idx == -1 && PyErr_Occurred()) {
             goto error;
         }
 
@@ -1178,7 +1178,12 @@ load_data(zoneinfo_state *state, PyZoneInfo_ZoneInfo *self, PyObject *file_obj)
         self->ttinfo_before = &(self->_ttinfos[0]);
     }
 
-    if (tz_str != Py_None && PyObject_IsTrue(tz_str)) {
+    int has_tz_str = PyObject_IsTrue(tz_str);
+    if (has_tz_str < 0) {
+        goto error;
+    }
+
+    if (has_tz_str) {
         if (parse_tz_str(state, tz_str, &(self->tzrule_after))) {
             goto error;
         }