custom: fix a memory leak when insert_group is ...
custom: fix a memory leak when insert_group is ...

custom: fix a memory leak when insert_group is called on a non-custom topology

(found by Coverity Scan)

This commit was SVN r5466.

shekkbuilder/hwloc,shekkbuilder/hwloc,ggouaillardet/hwloc,shekkbuilder/hwloc,ggouaillardet/hwloc,shekkbuilder/hwloc,ggouaillardet/hwloc,ggouaillardet/hwloc