ExifInterface: fix NegativeArraySizeException

The IFD entry has a 4-byte field COUNT. It is read as int type
and is used as array size by ExifInterface. If a crafted JPEG
file contains a negative value, a NegativeArraySizeException
occurs.

Test: passed ExifInterface CTS
Change-Id: Ief29936400f04636928df09e7f357cbf25345383
Signed-off-by: NIEJuhu <niejuhu@xiaomi.com>