highlight: do not add html classes to unresolved local variables
highlight: do not add html classes to unresolved local variables

Eg. this avoid highlighting to only highlight the fist occurrence of `x`
in the following AST if no semantic analysis is run

~~~
var x = 5
print x
~~~

Now, either none, or both `x` are identified as variables according to how
mush semantic analysis is performed.


Signed-off-by: Jean Privat <51f8b1fa9b424745378826727452997ee2a7c3d7@pryen.org>

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