Fixed highlighter resetting of syntax on doc filename change

data/core/doc/highlighter.lua

@@ -9,9 +9,7 @@ local Highlighter = Object:extend()
 
 function Highlighter:new(doc)
   self.doc = doc
-  self.lines = {}
+  self:reset()
-  self.first_invalid_line = 1
-  self.max_wanted_line = 0
 
   -- init incremental syntax highlighting
   core.add_thread(function()
@@ -40,6 +38,12 @@ function Highlighter:new(doc)
 end
 
 
+function Highlighter:reset()
+  self.lines = {}
+  self.first_invalid_line = 1
+  self.max_wanted_line = 0
+end
+
 function Highlighter:invalidate(idx)
   self.first_invalid_line = idx
   self.max_wanted_line = math.min(self.max_wanted_line, #self.doc.lines)

data/core/doc/init.lua

@@ -59,7 +59,7 @@ function Doc:reset_syntax()
   local syn = syntax.get(self.filename or "")
   if self.syntax ~= syn then
     self.syntax = syn
-    self.highlighter:invalidate(1)
+    self.highlighter:reset()
   end
 end