fix: add error handling for malformed timestamps in org-drill-entry-days-since-creation

Wrapped org-time-stamp-to-now call in condition-case to gracefully handle
malformed DATE_ADDED property values. Now returns nil instead of crashing
when encountering invalid timestamp formats.

Changes:
- Added condition-case around org-time-stamp-to-now (lines 2896-2898)
- Returns nil on error, allowing the function to fall through to other
  branches or return nil gracefully

This prevents unhandled errors in long-running sessions when drill entries
have corrupted or manually-edited timestamp values.

1 files changed, 3 insertions, 1 deletions

diff --git a/org-drill.el b/org-drill.el
index e1eea77..09e88b6 100644
--- a/org-drill.el
+++ b/org-drill.el
@@ -2893,7 +2893,9 @@ that many days)."
   (let ((timestamp (org-entry-get (point) "DATE_ADDED")))
     (cond
      (timestamp
-      (- (org-time-stamp-to-now timestamp)))
+      (condition-case nil
+          (- (org-time-stamp-to-now timestamp))
+        (error nil)))
      (use-last-interval-p
       (+ (or (org-drill-entry-days-overdue session) 0)
          (string-to-number (or (org-entry-get (point) "DRILL_LAST_INTERVAL") "0"))))