fix: Avoid signed ISO8601 length sentinel

Use 0 to request parsing the full null-terminated ISO8601 string. This keeps
call sites clean and avoids MSVC signed/unsigned conversion warnings.

Co-Authored-By: OpenAI Codex <noreply@openai.com>

Author: jpnurmi

src/sentry_session.c

@@ -182,7 +182,7 @@ sentry__session_from_json(const char *buf, size_t buflen)
     rv->errors = (uint64_t)sentry_value_as_int32(
         sentry_value_get_by_key(value, "errors"));
     rv->started_us = sentry__iso8601_to_usec(
-        sentry_value_as_string(sentry_value_get_by_key(value, "started")), -1);
+        sentry_value_as_string(sentry_value_get_by_key(value, "started")), 0);
 
     double duration
         = sentry_value_as_double(sentry_value_get_by_key(value, "duration"));

src/sentry_utils.c

@@ -481,7 +481,7 @@ sentry__usec_time_to_iso8601(uint64_t time)
 uint64_t
 sentry__iso8601_to_usec(const char *iso, size_t iso_len)
 {
-    size_t len = iso_len == (size_t)-1 ? sentry__guarded_strlen(iso) : iso_len;
+    size_t len = iso_len ? iso_len : sentry__guarded_strlen(iso);
     if (len != 20 && len != 27) {
         return 0;
     }

tests/unit/test_utils.c

@@ -21,9 +21,9 @@ SENTRY_TEST(iso_time)
     uint64_t usec;
     char *str;
 
-    usec = sentry__iso8601_to_usec("1970-01-01T00:00:10Z", -1);
+    usec = sentry__iso8601_to_usec("1970-01-01T00:00:10Z", 0);
     TEST_CHECK_INT_EQUAL(usec, 10 * 1000000);
-    usec = sentry__iso8601_to_usec("2020-04-27T11:02:36.050505Z", -1);
+    usec = sentry__iso8601_to_usec("2020-04-27T11:02:36.050505Z", 0);
     TEST_CHECK_INT_EQUAL(usec, 1587985356050505);
     str = sentry__usec_time_to_iso8601(usec);
     TEST_ASSERT(!!str);
@@ -33,7 +33,7 @@ SENTRY_TEST(iso_time)
     usec = sentry__usec_time();
     str = sentry__usec_time_to_iso8601(usec);
     TEST_ASSERT(!!str);
-    uint64_t roundtrip = sentry__iso8601_to_usec(str, -1);
+    uint64_t roundtrip = sentry__iso8601_to_usec(str, 0);
     sentry_free(str);
     TEST_CHECK_INT_EQUAL(roundtrip, usec);
 }