Clean up unnecessary git_buf_printf calls

This replaces some git_buf_printf calls with simple calls to
git_buf_put instead.  Also, it fixes a missing va_end inside
the git_buf_vprintf implementation.

src/buffer.c

@@ -211,6 +211,8 @@ int git_buf_vprintf(git_buf *buf, const char *format, va_list ap)
 			format, args
 		);
 
+		va_end(args);
+
 		if (len < 0) {
 			git__free(buf->ptr);
 			buf->ptr = git_buf__oom;

src/diff_print.c

@@ -336,7 +336,7 @@ static int diff_print_patch_hunk(
 		return 0;
 
 	git_buf_clear(pi->buf);
-	if (git_buf_printf(pi->buf, "%.*s", (int)header_len, header) < 0)
+	if (git_buf_put(pi->buf, header, header_len) < 0)
 		return -1;
 
 	if (pi->print_cb(d, r, GIT_DIFF_LINE_HUNK_HDR,
@@ -360,13 +360,14 @@ static int diff_print_patch_line(
 		return 0;
 
 	git_buf_clear(pi->buf);
+	git_buf_grow(pi->buf, content_len + 2);
 
 	if (line_origin == GIT_DIFF_LINE_ADDITION ||
 		line_origin == GIT_DIFF_LINE_DELETION ||
 		line_origin == GIT_DIFF_LINE_CONTEXT)
-		git_buf_printf(pi->buf, "%c%.*s", line_origin, (int)content_len, content);
-	else if (content_len > 0)
-		git_buf_printf(pi->buf, "%.*s", (int)content_len, content);
+		git_buf_putc(pi->buf, line_origin);
+
+	git_buf_put(pi->buf, content, content_len);
 
 	if (git_buf_oom(pi->buf))
 		return -1;