vconsole-setup: handle the case where the vc is in KD_GRAPHICS mode more gracefully

vconsole-setup: handle the case where the vc is in KD_GRAPHICS mode more gracefully

Regardless of whether a vc path is passed, the behavior of
systemd-vconsole-setup wasn't ideal when either the passed vc or /dev/tty1 was
in graphics mode.

When a vc in graphics mode was passed, no message was emitted despite the fact
that the font settings couldn't be applied. The previous code might have
assumed that setfont(8) would throw a warning but that's not case.

When no argument was passed, systemd-vconsole-setup was supposed to
automatically select a valid tty, init it and copy the font setting to the
remaining ttys. However if the selected virtual console was in KD_GRAPHICS mode
the initialization of the font failed not only for the selected source vc but
for all of them.