config --replace-all: avoid extra line breaks

When replacing multiple config entries at once, we did not re-set the
flag that indicates whether we need to insert a new-line before the new
entry. As a consequence, an extra new-line was inserted under certain
circumstances.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

config.c

@@ -2617,6 +2617,7 @@ int git_config_set_multivar_in_file_gently(const char *config_filename,
 			store.seen = 1;
 
 		for (i = 0, copy_begin = 0; i < store.seen; i++) {
+			new_line = 0;
 			if (store.offset[i] == 0) {
 				store.offset[i] = copy_end = contents_sz;
 			} else if (store.state != KEY_SEEN) {