Fix GH-7809: Cloning a faked SplFileInfo object may segfault

While the `path` is not supposed to be `NULL` for normal operation, it
is possible to create `SplFileInfo` objects where that

Fix GH-7809: Cloning a faked SplFileInfo object may segfault

While the `path` is not supposed to be `NULL` for normal operation, it
is possible to create `SplFileInfo` objects where that is the case, and
we must not follow the null pointer.

Closes GH-7814.

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