dict: Put "goto out" in dict_unserialize to avoid process crash

Problem:
In the dictionary serialization function, if the
[(buf + vallen) > (orig_buf + size)], then memdup is getting failed.

Fix:
Put "goto out" whenever this condition is met.

Change-Id: Ia10ddc7e1cf551eed0e2c3d0f0364c6961e13025
BUG: 947824
Signed-off-by: Venkatesh Somyajulu <vsomyaju@redhat.com>
Reviewed-on: http://review.gluster.org/4770
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Jeff Darcy <jdarcy@redhat.com>