Remove a blank line when a regtype is 'V' and a text object is entire buffer

When a regtype is 'V' and the object is entire buffer, a blank line remains at the top of buffer because a buffer of Vim has at least one line for the place of cursor. This problem often occurs when using vim-textobj-entire.

Before text is:
```
hoge huga
```

Then, do:
```vim
:call setreg('s', 'aaa', 'V') | execute 'normal' "V\"s\<Plug>(operator-replace)"
```

After text is:
```

aaa
```


This commit fixes the issue by dirty workaround.
I've **added** a test case to confirm that the issue is fixed.