Issue doing projection

Hi ! 

When trying to do a projection using Tools, Record Max-Projection Movie, it doesn’t produce anything and the console shows
```log
java.lang.NullPointerException
	at bdv.tools.RecordMaxProjectionDialog.recordMovie(RecordMaxProjectionDialog.java:372)
	at bdv.tools.RecordMaxProjectionDialog$4$1.run(RecordMaxProjectionDialog.java:249)
```

Would you happen to know why ? 

Best,
Laurent