Allow jvmti Allocate & Deallocate function on unattached threads

Some real-world agents will call the JVMTI Allocate and Deallocate
functions on unattached threads and expect them to function correctly.
We change the error checking to allow them to be used in this way. This
is to make it easier to debug possible issues with agents.

Test: ./test.py --host -j50
Bug: 70918330
Change-Id: If1796773b198d171284c3e02f38504bf094b9e0d