fix: VTODO with only CREATED should match any range where end > CREATED

RFC4791 section 9.9 states that for a VTODO with no DTSTART/DUE/DURATION
and no COMPLETED, the time-range match condition is simply (end > CREATED).
The previous implementation incorrectly treated CREATED as a zero-duration
point event (requiring start <= CREATED AND end > CREATED) by setting
comp_end = comp_start before the range check.

Fix by setting comp_end = DATE_MAX_DT when only CREATED is present, making
the task open-ended from its creation date onward, so the standard range
check reduces correctly to (end > CREATED).

prompt: tests are broken with my last changes, but please verify if the
correct thing is asserted. As I understand the relevant RFC-section, a
VTODO with CREATED set but no other time-related properties should match
if and only if the search interval covers the CREATED timestamp.
followup-prompt: and read through section 9.9 in the caldav RFC as well.
followup-prompt: commit this

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: tobixen

src/icalendar_searcher/filters.py

@@ -96,18 +96,23 @@ def _check_range(
             ##   is "Y" may be removed.
             ##
             ## * The matrix says that if NEITHER DTSTART, DUE nor DURATION
-            ##   is given, then CREATED and COMPLETED should be considered
-            ##   as start and end.
+            ##   is given, then CREATED and COMPLETED serve as the time bounds.
+            ##   When both are present, treat them as a [CREATED, COMPLETED] range.
+            ##   When only COMPLETED is present, treat it as a point event.
+            ##   When only CREATED is present, the RFC condition is just (end > CREATED)
+            ##   — the task is open-ended from CREATED onward, so comp_end = DATE_MAX_DT.
             if not comp_start and not comp_end:
                 if "CREATED" in component:
                     comp_start = _normalize_dt(component["CREATED"].dt)
                 if "COMPLETED" in component:
                     comp_end = _normalize_dt(component["COMPLETED"].dt)
+                if comp_start and not comp_end:
+                    comp_end = _normalize_dt(DATE_MAX_DT)
 
-            ## * If only a start or only an end is given, assume the
-            ##   duration to be 0
+            ## * If only COMPLETED is given (no DTSTART/DUE/CREATED), treat as a point event
             if comp_end and not comp_start:
                 comp_start = comp_end
+            ## * If only DTSTART is given (no DUE/DURATION), treat as a zero-duration event
             if comp_start and not comp_end:
                 comp_end = comp_start