patch 9.1.1259: some issues with comment package and tailing spaces

patch 9.1.1259: some issues with comment package and tailing spaces

Problem:  some issues with comment package and tailing spaces
Solution: correctly capture trailing spaces with the ac/ic text object
          (Maxim Kim)

This commit fixes a few issues with the comment package:

1) both ac and ic incorrectly miss the last //

```
// hello trailing spaces
//
```

2) fix ac/ic with last empty comment line,
   vac should also select last line with #

```py
 # print("hello")
 # print("world")
 #
 #
$endofbuffer$
```

closes: #17013

Signed-off-by: Maxim Kim <habamax@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>