'.lf 1 "-' gives wrong line numbers (1 to short) in diagnostics

[Bjarni Ingi Gislason]

'.lf 1 "-' was added as the first line to all man pages for the use in
"batch mode".

But the input line numbers shift then by 1 instead be 2, as the original
first line is now number 2.

Tested by changing macro call '.I' to '.IR' in a man page.