FileHandle: don't unnecessarily init a RandomAccessFile on close

If we close a handle on a file that does not exist, we do not need to
initialize the RandomAccessFile, just to close it again. This fixes the problem of
empty files appearing when closing a FileHandle to a file that does not exist.

Author: Gabriel Einsdorf

src/main/java/org/scijava/io/handle/FileHandle.java

@@ -290,7 +290,7 @@ public void writeUTF(final String str) throws IOException {
 
 	@Override
 	public void close() throws IOException {
-		raf().close();
+		if (raf != null) raf().close();
 	}
 
 	// -- Typed methods --