vis: abort syntax highlighting if viewport is invalid

In theory this should not happen in the first place, but in practice it
might fix the symptoms reported in issue #367.

1 files changed, 3 insertions, 0 deletions

diff --git a/vis.lua b/vis.lua
index f4a5232..c8d1bb3 100644
--- a/vis.lua
+++ b/vis.lua
@@ -345,6 +345,9 @@ vis.events.win_highlight = function(win, horizon_max)
 
 	-- TODO: improve heuristic for initial style
 	local viewport = win.viewport
+	if not viewport then
+		return
+	end
 	local horizon = viewport.start < horizon_max and viewport.start or horizon_max
 	local view_start = viewport.start
 	local lex_start = viewport.start - horizon