Fix bug where canceling an autocomplete could delete a previously confirmed completion

spec/extensions/autocomplete-spec.coffee

@@ -167,6 +167,19 @@ describe "Autocomplete", ->
       expect(editor.getSelection().getBufferRange()).toEqual originalSelectionBufferRange
       expect(editor.find('.autocomplete')).not.toExist()
 
+    fit "does not clear out a previously confirmed selection when canceling with an empty list", ->
+      editor.buffer.insert([10, 0], "sort\n")
+      editor.setCursorBufferPosition([10, 0])
+
+      autocomplete.attach()
+      miniEditor.trigger 'autocomplete:confirm'
+      expect(editor.lineForBufferRow(10)).toBe 'quicksort'
+
+      editor.setCursorBufferPosition([11, 0])
+      autocomplete.attach()
+      miniEditor.trigger 'autocomplete:cancel'
+      expect(editor.lineForBufferRow(10)).toBe 'quicksort'
+
   describe 'move-up event', ->
     it "highlights the previous match and replaces the selection with it", ->
       editor.buffer.insert([10,0] ,"extra:t:extra")

src/extensions/autocomplete.coffee

@@ -104,6 +104,7 @@ class Autocomplete extends View
 
     @originalSelectedText = @editor.getSelectedText()
     @originalSelectionBufferRange = @editor.getSelection().getBufferRange()
+    @currentMatchBufferRange = null
     @allMatches = @findMatchesForCurrentSelection()