Fix usage of SQLite::Database constructor with null vfs
Fix usage of SQLite::Database constructor with null vfs

Seems that make_unique was inferring the Database constructor that takes a string& for the vfs,
so passing NULL made it try to construct a string from that, which causes a segfault.

cleeus/tangram-es,cleeus/tangram-es,tangrams/tangram-es,cleeus/tangram-es,tangrams/tangram-es,cleeus/tangram-es,cleeus/tangram-es,quitejonny/tangram-es,quitejonny/tangram-es,quitejonny/tangram-es,tangrams/tangram-es,tangrams/tangram-es,tangrams/tangram-es,cleeus/tangram-es,quitejonny/tangram-es,quitejonny/tangram-es,quitejonny/tangram-es,tangrams/tangram-es,tangrams/tangram-es