Fix region boundary cache lookup segfault

When the cursor position is after the last item in the vector,
upper_bound returns the last given iterator, here:
`region_boundary_cache.end()`, which is invalid to dereference.

Furthermore prevent possible  duplicate prev/next pair at zero,
when using the video-timelime.

2 files changed, 8 insertions, 2 deletions

diff --git a/gtk2_ardour/editor.cc b/gtk2_ardour/editor.cc
index a6b5a34d49..584a007302 100644
--- a/gtk2_ardour/editor.cc
+++ b/gtk2_ardour/editor.cc
@@ -2995,6 +2995,9 @@ Editor::snap_to_internal (MusicSample& start, RoundMode direction, SnapPref pref
 				prev = next;
 				prev--;
 			}
+			if (next == region_boundary_cache.end ()) {
+				next--;
+			}
 
 			if ((direction == RoundUpMaybe || direction == RoundUpAlways)) {
 				test = *next;
diff --git a/gtk2_ardour/editor_ops.cc b/gtk2_ardour/editor_ops.cc
index ead64e378d..2c0d3bcdee 100644
--- a/gtk2_ardour/editor_ops.cc
+++ b/gtk2_ardour/editor_ops.cc
@@ -768,9 +768,12 @@ Editor::build_region_boundary_cache ()
 		}
 	}
 
-	//allow regions to snap to the video start (if any) as if it were a "region"
+	/* allow regions to snap to the video start (if any) as if it were a "region" */
 	if (ARDOUR_UI::instance()->video_timeline) {
-		region_boundary_cache.push_back (ARDOUR_UI::instance()->video_timeline->get_video_start_offset());
+		ARDOUR::samplepos_t vo = ARDOUR_UI::instance()->video_timeline->get_video_start_offset();
+		if (std::find (region_boundary_cache.begin(), region_boundary_cache.end(), vo) == region_boundary_cache.end()) {
+			region_boundary_cache.push_back (ARDOUR_UI::instance()->video_timeline->get_video_start_offset());
+		}
 	}
 
 	std::pair<samplepos_t, samplepos_t> ext = session_gui_extents (false);