Fixed reuse of directory-IDs after moving encrypted directories but keeping references to the old locations.

This caused an illegal state where two different directories share the same directory id, making further file operations on these directories virtually impossible.

main/filesystem-inmemory/src/main/java/org/cryptomator/filesystem/inmem/InMemoryFile.java

@@ -69,6 +69,7 @@ class InMemoryFile extends InMemoryNode implements File {
 					throw new UncheckedIOException(new FileAlreadyExistsException(k));
 				} else {
 					if (v == null) {
+						assert!content.hasRemaining();
 						this.creationTime = Instant.now();
 					}
 					this.lastModified = Instant.now();