Fix restoring to graphics modes in VGLEnd().

Correct restoring was only attempted for mode 258 (800x600x4 P). (This
was the only useful graphics mode supported in the kernel until 10-15
years ago, and is still the only one explicitly documented in the man
page). The comment says that it is the geometry (subscreen size) that
is restored, but it seems to only be necessary to restore the font
size, with the geometry only needed since it is set by the same ioctl.
The font size was not restored for this mode, but was forced to 16.

For other graphics modes, the font size was clobbered to 0. This
confuses but doesn't crash the kernel (font size 0 gives null text).
This confuses and crashes vidcontrol. The only way to recover was to
use vidcontrol to set the mode to any text mode on the way back to the
original graphics mode.

vidcontrol gets this wrong in the opposite way when backing out of
changes after an error. It restores the font size correctly, but
forces the geometry to the full screen size.