In the zipvfile extension (which is not part of the SQLite amalgamation, but

which is included in the CLI by default) ensure that fopen() is not invoked
using a NULL filename.  Fix for the issue reported by
[forum:/forumpost/d1c96a9032e564f8|forum post d1c96a9032e564f8].

FossilOrigin-Name: d32757ddf5d311b6f62545c861fd606244e03f02cb2e317c1131ee6b80c2299c