input: don't drop the first byte when user starts typing during loading

Precalculation of the multiline color data can be cut short when the
user is impatient and starts typing.  But this would drop the first
byte of whatever was typed -- not nice when it was just plain text,
but surprising and worse when the first keystroke was a command.

This fixes https://savannah.gnu.org/bugs/?48388.
1 file changed