Fix cursor in empty comment input in Safari

[MorrisJobke]

Followup to #7800

See #7800 (comment)

The empty input has a too big cursor in Safari:

See also this thread https://stackoverflow.com/a/9132362

I could also not figure out how to enforce this without the display: block;, font-size, line-heightand height all didn't worked out :/

cc @Abijeet

[Abijeet]

Hi @MorrisJobke,

Please find the merge request here - #9184. I reproduced the issue on BrowserStack - Safari 7.1 and verified that the fix I've made works (at-least there).