Fix double-freeing of ScopedAResource

Default move constructor didn't reset mT to nullptr, which caused double
freeing of mT when returning ScopedAResource without NRVO. Fixing the
bug by resetting mT to its default value.

Test: atest under cts/tests/tests/binder_ndk
Change-Id: I04c874f802d8f88fa5f495776c00f7e2f74db094