libgltf: solve this memory leak problem on a better way 2

Handle those cases when file loading failes.
Release *.json file on a different way since it is allocated
by libgltf (inside the glTFHandle).

(cherry picked from commit fafc1e29c1f060c1a44361a0445300f9786ad6f4)

Change-Id: Idf6c6971a8ac1b342d89dc4f61a62624183e01d0