Avoid consuming lots of space and time if the first partition is not near the start of the disk (Debian bug #619458, Ubuntu bug #691569).

grub-core/partmap/gpt.c

@@ -125,6 +125,7 @@ gpt_partition_map_iterate (grub_disk_t disk,
 #ifdef GRUB_UTIL
 static grub_err_t
 gpt_partition_map_embed (struct grub_disk *disk, unsigned int *nsectors,
+			 unsigned int max_nsectors,
 			 grub_embed_type_t embed_type,
 			 grub_disk_addr_t **sectors)
 {
@@ -174,6 +175,8 @@ gpt_partition_map_embed (struct grub_disk *disk, unsigned int *nsectors,
 		       " embedding won't be possible!");
 
   *nsectors = len;
+  if (*nsectors > max_nsectors)
+    *nsectors = max_nsectors;
   *sectors = grub_malloc (*nsectors * sizeof (**sectors));
   if (!*sectors)
     return grub_errno;