Replace calls to strbuf_init(&foo, 0) with STRBUF_INIT initializer

Many call sites use strbuf_init(&foo, 0) to initialize local
strbuf variable "foo" which has not been accessed since its
declaration. These can be replaced with a static initialization
using the STRBUF_INIT macro which is just as readable, saves a
function call, and takes up fewer lines.

Signed-off-by: Brandon Casey <casey@nrlssc.navy.mil>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
diff --git a/builtin-tag.c b/builtin-tag.c
index f2853d0..b13fa34 100644
--- a/builtin-tag.c
+++ b/builtin-tag.c
@@ -338,7 +338,7 @@
 
 int cmd_tag(int argc, const char **argv, const char *prefix)
 {
-	struct strbuf buf;
+	struct strbuf buf = STRBUF_INIT;
 	unsigned char object[20], prev[20];
 	char ref[PATH_MAX];
 	const char *object_ref, *tag;
@@ -388,7 +388,6 @@
 	if (verify)
 		return for_each_tag_name(argv, verify_tag);
 
-	strbuf_init(&buf, 0);
 	if (msg.given || msgfile) {
 		if (msg.given && msgfile)
 			die("only one -F or -m option is allowed.");