Handle error result returned from MTP API correctly.

 * Check null result for all MTP APIs that can return null.
 * Don't regard valid parent handles that are more than 0x80000000 as
   error.
 * Check boolean result from importFile.

Change-Id: I262511ac3c935ebb54e52c03eaefd3535a3e2f29
Fix: 28155538
1 file changed