Use correct type for GetValueFromShadowFrame

The field type is not necessarily the input type for boxed
primitives. If the field type is < 32 bits, it means there will be
partial object pointer in the JValue. If a conversion check is
later needed in GetUnboxedTypeAndValue, it will crash. The fix is
to use the PTypes.

Bug: 37446461
Test: test-art-host

(cherry picked from commit 71b1708f)

Change-Id: I4da1e44368488bee8528e6406fc20532048a9569