virDomainMachineNameAppendValid: Handle special characters better

virDomainMachineNameAppendValid: Handle special characters better

When constructing guest name for machined we have to be very
cautious as machined expects a name that's basically a valid URI.
Therefore, if there's a dot it has to be followed by a letter or
a number. And if there's a sequence of two or more dashes they
should be joined into a single dash. These rules are implemented
in virDomainMachineNameAppendValid(). There's the @skip variable
which is supposed to track whether it is safe to append a dot or
a dash into name. However, the variable is set to false (meaning
it is safe to append a dot or a dash) even if the current
character we are processing is not in the set of allowed
characters (and thus skipped over).

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1948433
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Daniel Henrique Barboza <danielhb413@gmail.com>