Fix dexlayout manual walking of 0 length catch handler.

This fails for 0 length handlers that are unreferenced by any try
blocks. Unreferenced handlers are handled differently and walked
manually, and there was an error in the 0 size case, when there is only
a single catch all handler.

Bug: 35874292
Test: mm test-art-host-gtest-dexlayout_test
Change-Id: Ie061b4fd0e7e8be7e3e382b11d2606f5ffc0817a