Fix test to search for a populated StackMap.

With the baseline compiler, the test could have hit a stack map for a
NullCheck, where we don't populate the reference StackMask in the stack
map. To fix this, look for another stack map starting at the same dex
pc.

Test: 004-ReferenceMap

Change-Id: I2628ded5c89c6fb0059a18341bffda78ef06f197
3 files changed