empty partition causes error for up_list

[saliola]

sage: p = Partition([])
sage: p.up_list()
Traceback ...
...
IndexError: list index out of range

Depends on #11300

CC: @sagetrac-sage-combinat

Component: combinatorics

Keywords: combinat, partitions, days30

Author: Jason Bandlow

Reviewer: Franco Saliola

Merged: sage-4.7.1.alpha1

Issue created by migration from https://trac.sagemath.org/ticket/11301

[jbandlow]

Attachment: trac_11301-uplist_fails_on_empty_partition-jb.patch.gz

[jbandlow]

Author: Jason Bandlow

[jbandlow]

Description changed:

--- 
+++ 
@@ -6,3 +6,4 @@
 ...
 IndexError: list index out of range
 ```
+

[jbandlow]

Dependencies: #11300

[jbandlow]

comment:2

Notice the dependency on 11300.

[saliola]

Reviewer: Franco Saliola

[hivert]

comment:4

Replying to @saliola:

Shouldn't we rename up_list to something more meaningful ? What about young_lattice_successors ?

Florent