Zero-initialize CursorWindow buffer

Zero-initialize mData in CursorWindow::create().  The caller might not
fully fill that buffer before sending it to the remote end.  It is not
necessary to zero-initialize in CursorWindow::createFromParcel(),
since the buffer is immediately filled from the far end.

Flag: EXEMPT bug-fix
Bug: 309407957
Test: atest
 * libandroidfw_tests
 * FrameworksCoreTests:android.database
 * CtsDatabaseTestCases
Change-Id: I755240b0e3ba185c01036a5e00c8785d2e1ac11a