Make the code in this function work even with wxFileSystemHandlers that
don't implement FindFirst() at all: we can, and should, still try
loading the passed in path with them, rather than not doing anything at
all.
This makes Load() works with HTTP URLs again, as it apparently used to
do a long time ago, but didn't do any more.
Add a unit test, even if only a semi-manual one, to try to help with
this not getting broken again (ideal would be to launch our own HTTP
server inside the test, but this is a bit more complicated).
Closes#19109.
9e96ff972b