Ensure GetSourceDebugExtension works with Proxy classes.

We were unconditionally trying to read a class-def pointer from
classes passed to GetSourceDebugExtension but this pointer will be
null for proxy classes. This could cause segfaults.

Bug: 67836742
Bug: 68157595

Test: ./test.py --host -j50
Change-Id: I3d9ee4647b65bf5092de486903c7fb1e88c718a5
4 files changed