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-checkout-index.c b/builtin-checkout-index.c
index 55b7aaf..4ba2702 100644
--- a/builtin-checkout-index.c
+++ b/builtin-checkout-index.c
@@ -268,13 +268,11 @@
 	}
 
 	if (read_from_stdin) {
-		struct strbuf buf, nbuf;
+		struct strbuf buf = STRBUF_INIT, nbuf = STRBUF_INIT;
 
 		if (all)
 			die("git checkout-index: don't mix '--all' and '--stdin'");
 
-		strbuf_init(&buf, 0);
-		strbuf_init(&nbuf, 0);
 		while (strbuf_getline(&buf, stdin, line_termination) != EOF) {
 			const char *p;
 			if (line_termination && buf.buf[0] == '"') {