RFR(XS): 6910461: Register allocator may insert spill code at wrong insertion index

[Roland Westrelin]

When resolving exception edges after register allocation, the C1 register allocator may insert spill code at the wrong insertion position due to an off-by-one error. This doesn't lead to any crash/failure with the current code because the exception handler is never empty but this change makes it consistent with the other uses of the same code.

http://cr.openjdk.java.net/~roland/6910461/webrev.00/

Roland.