[MTBF]Tombstone on com.android.browser at /system/lib/libskia.so

if given a null bitmap to encode, the function will be failed, now we check
the given picture.

Change-Id: Iea12db55165817e64339135e60a1afca6dec0979
Author: Weiwei Ji <weiweix.ji@intel.com>
Signed-off-by: Weiwei Ji <weiweix.ji@intel.com>
Signed-off-by: Shuo Gao <shuo.gao@intel.com>
Signed-off-by: Bruce Beare <bruce.j.beare@intel.com>
Signed-off-by: Jack Ren <jack.ren@intel.com>
Author-tracking-BZ: 38891