Syntax highlighting for #_ forms comments out next form

## Expected behavior

When using the `#_` reader macro, you can chain several together. This lets you comment out more than one form at a time. However the Cider syntax highlighting uses the first `#_` to comment out the second one. For example:

In Cursive:

## Actual behavior

In emacs:

## Steps to reproduce the problem

``` clj
#_ #_ :a :b
```
## Environment & Version information
### clojure-mode version information

```
clojure-mode (version 5.5.2)
```
### Emacs version

`25.1.50.1`
### Operating system

OS X 10.11.6

Carried over from https://github.com/clojure-emacs/cider/issues/1822

Start by reproducing the issue in clojure-mode with `#_ #_ :a :b` and inspect the syntax-highlighting behavior described in the report. Done means chained `#_` forms are highlighted independently, so the first reader macro does not incorrectly consume the second one.

Scritto dal modello di indicizzazione a partire dal testo della issue.