ART: Use null for the BootClassLoader in LoadLibrary

We must translate the fake BootClassLoader object to the internally
used null when loading libraries.

Bug: 29449194
Test: test-art-host

(cherry picked from commit f7e0db0ce1170b88043f7eb6afcc93c861c4611d)

Change-Id: I823d34e209149b5b96529a423c60a1d77bf8e9d1
4 files changed