use child_process_init() to initialize struct child_process variables

Call child_process_init() instead of zeroing the memory of variables of
type struct child_process by hand before use because the former is both
clearer and shorter.

Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/column.c b/column.c
index 8082a94..786abe6 100644
--- a/column.c
+++ b/column.c
@@ -374,7 +374,7 @@
 	if (fd_out != -1)
 		return -1;
 
-	memset(&column_process, 0, sizeof(column_process));
+	child_process_init(&column_process);
 	argv = &column_process.args;
 
 	argv_array_push(argv, "column");