[MTP] fix an ArrayIndexOutOfBoundsException

The object's file path may include more than 255 characters that is
out of MTP string limitation and this will casue a exception
"ArrayIndexOutOfBoundsException". This patch add checking for the
string length of path.

Change-Id: I74ca12e2bccd5f4644aadc79904fa0f3a3415a2a
Author: Changbin Du <changbinx.du@intel.com>
Signed-off-by: Changbin Du <changbinx.du@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: 56769