8029018: (bf) Check src/share/native/java/nio/Bits.c for JNI pending excepitons

[Alan Bateman]

This is trivial update to Bits.c to squash a warning of potential JNI 
usage when there is a pending exception. This is the code that is used 
when copying between direct buffers of different endianness. The warning 
is that GetPrimitiveArrayCritical could potentially fail (with a pending 
exception) although in the case of HotSpot then I don't think this is 
possible so this change is really just to squash the warning.

The webrev with the change is here:

http://cr.openjdk.java.net/~alanb/8029018/webrev/

-Alan.