Die for an early EOF in a file reading loop

The resulting data is zero terminated after the read loop, but
the subsequent loop that scans for '\n' will overrun the buffer.

Signed-off-by: Heikki Orsila <heikki.orsila@iki.fi>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

combine-diff.c

@@ -718,9 +718,9 @@ static void show_patch_diff(struct combine_diff_path *elem, int num_parent,
 			result = xmalloc(len + 1);
 			while (sz < len) {
 				ssize_t done = xread(fd, result+sz, len-sz);
-				if (done == 0)
-					break;
-				if (done < 0)
+				if (done == 0 && sz != len)
+					die("early EOF '%s'", elem->path);
+				else if (done < 0)
 					die("read error '%s'", elem->path);
 				sz += done;
 			}