[11.x] Fix join_paths issue with segment '0'

[imanghafoori1]

since the join_paths() function internally uses the empty function to filter out empty strings and prevent double slashes in the end result, it also filters out a perfectly valid path segment with the value of '0'.
empty('0'); // true
empty(''); // true

a folder with the name "0" is perfectly valid in Windows and UNIX, so there is no reason to delete 0 from segments while joining them.

Backward compatibility:

This is not in theory backward compatible but statistically very rare to happen and very rare for an application to rely on this flaw to work correctly.