Fix off-by-1 error in vfscanf

Scanf function requires look ahead to function properly, In case of
scanning from a buffer that will not be an issue, but in our case we are
reading from file, so lookaheads needs to be undone (via lseek) in our
case. The only problem here is that if we opened a file that doesn't
support lseek such as many of the file /dev/*