[PATCH resubmit] Assemble: prevent segfault with faulty "best" devices

[Andrea Righi <righi.andrea@gmail.com>]

In Assemble(), after context reload, best[i] can be -1 in some cases,
and before checking if this value is negative we use it to access
devices[j].i.disk.raid_disk, potentially causing a segfault.

Check if best[i] is negative before using it to prevent this potential
segfault.

Regression was causes by commit 69a481166be6 ("Assemble array with write
journal").

Reviewed-by: NeilBrown <neilb@suse.com>
Signed-off-by: Andrea Righi <andrea@betterlinux.com>
Signed-off-by: Robert LeBlanc <robert@leblancnet.us>
---
 Assemble.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Assemble.c b/Assemble.c
index 3da0903..fc681eb 100644
--- a/Assemble.c
+++ b/Assemble.c
@@ -1669,6 +1669,8 @@ try_again:
 		int j = best[i];
 		unsigned int desired_state;
 
+		if (j < 0)
+			continue;
 		if (devices[j].i.disk.raid_disk == MD_DISK_ROLE_JOURNAL)
 			desired_state = (1<<MD_DISK_JOURNAL);
 		else if (i >= content->array.raid_disks * 2)
@@ -1678,8 +1680,6 @@ try_again:
 		else
 			desired_state = (1<<MD_DISK_ACTIVE) | (1<<MD_DISK_SYNC);
 
-		if (j<0)
-			continue;
 		if (!devices[j].uptodate)
 			continue;