[BUGFIX] Copying directories is impossible

Due to a bug introduced with a refactoring of t3lib_extFileFunc, it
became impossible to copy directories. The two wrong statements (they
were not inverted though they should have been) are fixed with this
commit.

Change-Id: Iaac9cbcf30e2b73e2fd7f5df6986e1ccdf76c079
Resolves: #30213
Related: #24218
Releases: 4.6
Reviewed-on: http://review.typo3.org/5241
Reviewed-by: Markus Klein
Reviewed-by: Philipp Gampe
Tested-by: Philipp Gampe
Tested-by: Markus Klein
Reviewed-by: Xavier Perseguers
Tested-by: Xavier Perseguers