RFR(XS) 8191854: Null pointer dereference in methodData.hpp:462

[dean.long at oracle.com]

https://bugs.openjdk.java.net/browse/JDK-8191854
http://cr.openjdk.java.net/~dlong/8191854/webrev/

This fixes a possible null pointer dereference here:

           int count = mdo->bci_to_data(branch_bci)->as_JumpData()->taken();
           tty->print_cr("back branch count = %d", count);

if bci_to_data() returns NULL.

dl