Fix T83869: Crash when creating Sequencer in new scene

Crash on null dereference in `SEQ_timeline_boundbox()`. This function was
generalized in rB9e4a4c2e996c to work on arbitrary `seqbase`.

Fixed by refactoring `SEQ_timeline_boundbox()` functions to return default
sane values if `seqbase` is `NULL`

Reviewed By: HooglyBoogly

Differential Revision: https://developer.blender.org/D9878

1 files changed, 14 insertions, 0 deletions

diff --git a/source/blender/sequencer/intern/sequencer.c b/source/blender/sequencer/intern/sequencer.c
index 82971a30c31..87b608ef141 100644
--- a/source/blender/sequencer/intern/sequencer.c
+++ b/source/blender/sequencer/intern/sequencer.c
@@ -327,6 +327,20 @@ void SEQ_tool_settings_fit_method_set(Scene *scene, eSeqImageFitMethod fit_metho
   tool_settings->fit_method = fit_method;
 }
 
+/**
+ * Get seqbase that is being viewed currently. This can be main seqbase or meta strip seqbase
+ *
+ * \param ed: sequence editor data
+ * \return pointer to active seqbase. returns NULL if ed is NULL
+ */
+ListBase *SEQ_active_seqbase_get(const Editing *ed)
+{
+  if (ed == NULL) {
+    return NULL;
+  }
+
+  return ed->seqbasep;
+}
 /** \} */
 
 /* -------------------------------------------------------------------- */