RFR(XS): 8147386: assert(size == calc_size) failed: incorrect size calculattion x86_32.ad

[Roland Westrelin]

http://cr.openjdk.java.net/~roland/8147386/webrev.00/

src_offset/dst_offset are incremented in the size computation code and then used if cbuf is not null but now have the wrong value.

Roland.