[display] completion should never be allowed to trigger in comments

Not sure if the test case works like this, it probably throws a "no completion point found" exception? But you get the idea.

Also, can't have a test case for doc comments for obvious reasons. :D

```haxe
package cases;

class Issue7050 extends DisplayTestCase {
/**
class Main {
static function main() {
// {-1-}
}
}
**/
function test() {
eq(0, toplevel(pos(1)).length);
}
}
```