Fix bugs that prevent from using AppFuse.

 * Allow buffer size that is greater than requested read size in JNI,
   because we reuse fixed-size buffer among multiple requests.
 * Fix condition to check if the file size is greater than 4GB or
   not. We need to use 0xffffffffl instead of 0xffffffff because
   0xffffffff is int and its value is -1.

BUG=None
Change-Id: I155916e139353b15dc1ab535234faf50d942996d