configure.ac: properly unset NEEDS_SSL_WITH_CRYPTO when sha1 func is missing

configure.ac: properly unset NEEDS_SSL_WITH_CRYPTO when sha1 func is missing

The empty assignment NEEDS_SSL_WITH_CRYPTO= was mistakenly paired with the
assignment NEEDS_SSL_WITH_CRYPTO=YesPlease in the "action-if-found"
parameter of the AC_CHECK_LIB macro.  The empty assignment was intended for
the "action-if-not-found" section, since in that case, the necessary sha1
hash function was not found and the internal sha1 implementation will be
used instead.

Signed-off-by: Brandon Casey <drafnel@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>