Create synthetic iterator boundaries between open and close tags

If no non-negative integer exists between an open and close tag code,
we still need to report a boundary there, since close tags always have
to come first at any given iterator position.

:pear:ed with @as-cii

src/tokenized-buffer-iterator.coffee

@@ -28,7 +28,11 @@ class TokenizedBufferIterator
       else
         scopeName = @grammarRegistry.scopeForId(tag)
         if tag % 2 is 0
-          @closeTags.push(scopeName)
+          if @openTags.length > 0
+            @tagIndex = index
+            break
+          else
+            @closeTags.push(scopeName)
         else
           @openTags.push(scopeName)
 
@@ -56,7 +60,10 @@ class TokenizedBufferIterator
         else
           scopeName = @grammarRegistry.scopeForId(tag)
           if tag % 2 is 0
-            @closeTags.push(scopeName)
+            if @openTags.length > 0
+              break
+            else
+              @closeTags.push(scopeName)
           else
             @openTags.push(scopeName)
         @tagIndex++