Check the `sectors' vector length before use it

Hi all,

I noticed that the "btrfs-debug-tree -e DEVICE" command returns an empty list. If it is a normal behaviour then this trivial patch solves a problem in the show-blocks program, where the `sectors' vector is used even in the case its length is zero.

Regards,
Giuseppe

From: Giuseppe Scrivano <[email protected]>
Date: Sun, 26 Jul 2009 23:12:38 +0200
Subject: [PATCH] Check the vector length before use it

---
 show-blocks |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

index 0164be9..c6cdc12 100755
@@ -228,7 +228,7 @@ shapeit(data)
 sectors = data[:,0]
 sizes = data[:,1]
 datalen = len(data)
-sectormax = numpy.max(sectors)
+sectormax = numpy.max(sectors) if len(sectors) > 0 else 0
 sectormin = 0
 num_cells = 800
 total_cells = num_cells * num_cells

1.6.3.3