Adjust safepoint position of implicit null checks.

The safepoint records stack masks and register masks. For implicit
null checks, they need to have their position to the instruction
doing the null check (the next one).

Test: org.apache.harmony.tests.java.io.BufferedWriterTest#test_write_LStringII_Exception
Change-Id: I347d9fe38fb9df23fbc00f9aa36f1ee9c54bf912
2 files changed