shortlog: fix wrapping lines of wraplen

shortlog: fix wrapping lines of wraplen

A recent commit [1] fixed a off-by-one wrapping error.  As a
side-effect, the conditional in add_wrapped_shortlog_msg() to decide
whether to append a newline needs to be removed.  The function
should always append a newline, which was the case before the
off-by-one fix, because strbuf_add_wrapped_text() never returns a
value of wraplen; when it returns wraplen, the string does not end
with a newline, so this caller needs to add one anyway.

[1] 14e1a4e1ff70aff36db3f5d2a8b806efd0134d50 utf8: fix off-by-one
    wrapping of text

Signed-off-by: Steffen Prohaska <prohaska@zib.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>