RelativeDate: Fix parsing of invalid strings

PRETIXEU-1NH

src/pretix/base/reldate.py

@@ -103,11 +103,18 @@ class RelativeDateWrapper:
             else:
                 timeparts = parts[2].split(':')
                 time = datetime.time(hour=int(timeparts[0]), minute=int(timeparts[1]), second=int(timeparts[2]))
-            data = RelativeDate(
-                days_before=int(parts[1] or 0),
-                base_date_name=parts[3],
-                time=time
-            )
+            try:
+                data = RelativeDate(
+                    days_before=int(parts[1] or 0),
+                    base_date_name=parts[3],
+                    time=time
+                )
+            except ValueError:
+                data = RelativeDate(
+                    days_before=0,
+                    base_date_name=parts[3],
+                    time=time
+                )
         else:
             data = parser.parse(input)
         return RelativeDateWrapper(data)