Fix GH-16390: dba_open() can segfault for "pathless" streams

`dba_open()` accepts arbitrary stream wrapper paths, but unless no
locking (`-`) is specified, we try to determine the underl

Fix GH-16390: dba_open() can segfault for "pathless" streams

`dba_open()` accepts arbitrary stream wrapper paths, but unless no
locking (`-`) is specified, we try to determine the underlying file
path. If that fails, we need to error out.

Closes GH-16498.

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