bug#34939: Some minibuffer behaviour is annoying

[Juri Linkov]

>> There is another place where messages conceal the minibuffer:
>> running a version-control command that asks for a branch name
>> and typing TAB for completion runs a command to fetch branch names.
>> Its output conceals the minibuffer when vc-command-messages is non-nil.
>> Here is a fix:
>
> The patch is okay

Pushed to master.