UIA/keyboard shortcut: do not append two spaces if access key is there but accelerator key isn't #6790

Hi,

In some cases (such as in Outlook 2016 ribbon), controls have access keys but not accelerator keys. If so, two spaces are appended. This should tno be done in order to not waste string real estte.

Note: the PR for it will be part of the PR for #6779. Thanks.