common: Strip trailing CR,LF from w32_strerror.

* common/stringhelp.c (w32_strerror): Strip trailing CR,LF.
* common/iobuf.c (iobuf_get_filelength): Use -1 and not 0 for the
arg to w32_strerror.

This is in particular annoying since we started to use a string
argument sanitizer in the logging code. Before that we just add an
extra blank line.

The second patch corrects a never yet seen error message.

• Signed-off-by: Werner Koch <wk@gnupg.org>