Fixed segfault if nine-patch image failed to load

Fixed segfault if nine-patch image failed to load

[problem]      If nine patch image fails to load, e.g. file not found,
then empty bitmap pointer is accessed when image actor tries to use it.
[cause]        Not checking bitmap pointer before dereference
[solution]     Ensured bitmap pointers are checked, if NULL, then an error is logged.

Change-Id: If42d2db4f662fc2323057f71b365a741e254d125
Signed-off-by: David Steele <david.steele@partner.samsung.com>