Fixed empty directory traversal

cmake/NiceModules.cmake

@@ -33,7 +33,9 @@ MACRO(SUBDIRREC result curdir)
 			SET(dirlist ${dirlist} ${to_add_rel})
 		ENDIF()
 	ENDFOREACH()
-	LIST(REMOVE_DUPLICATES dirlist)
+	IF(NOT "${dirlist}" MATCHES "")
+		LIST(REMOVE_DUPLICATES dirlist)
+	ENDIF()
 	SET(${result} ${dirlist})
 ENDMACRO()