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.

1 files changed, 5 insertions, 2 deletions

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);