http-backend: Fix bad treatment of uintmax_t in Content-Length

Our Content-Length needs to report an off_t, which could be larger
precision than size_t on this system (e.g. 32 bit binary built with
64 bit large file support).

We also shouldn't be passing a size_t parameter to printf when
we've used PRIuMAX as the format specifier.

Fix both issues by using uintmax_t for the hdr_int() routine,
allowing strbuf's size_t to automatically upcast, and off_t to
always fit.

Also fixed the copy loop we use inside of send_local_file(), we never
actually updated the size variable so we might as well not use it.

Reported-by: Tarmigan <tarmigan+git@gmail.com>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

http-backend.c

diff --git a/http-backend.c b/http-backend.c
index f8ea9d7..7f48406 100644
--- a/http-backend.c
+++ b/http-backend.c
@@ -134,7 +134,7 @@
 	format_write(1, "%s: %s\r\n", name, value);
 }
 
-static void hdr_int(const char *name, size_t value)
+static void hdr_int(const char *name, uintmax_t value)
 {
 	format_write(1, "%s: %" PRIuMAX "\r\n", name, value);
 }
@@ -216,7 +216,6 @@
 	char *buf = xmalloc(buf_alloc);
 	int fd;
 	struct stat sb;
-	size_t size;
 
 	fd = open(p, O_RDONLY);
 	if (fd < 0)
@@ -224,14 +223,12 @@
 	if (fstat(fd, &sb) < 0)
 		die_errno("Cannot stat '%s'", p);
 
-	size = xsize_t(sb.st_size);
-
-	hdr_int(content_length, size);
+	hdr_int(content_length, sb.st_size);
 	hdr_str(content_type, the_type);
 	hdr_date(last_modified, sb.st_mtime);
 	end_headers();
 
-	while (size) {
+	for (;;) {
 		ssize_t n = xread(fd, buf, buf_alloc);
 		if (n < 0)
 			die_errno("Cannot read '%s'", p);