[NbtkTable] don't allocate children less than their minimum height
[NbtkTable] don't allocate children less than their minimum height

This prevents children from being allocated less than their minimum height.

pwithnall/mx,pwithnall/mx,pwithnall/mx,clutter-project/mx,clutter-project/mx,jonnylamb/mx,jonnylamb/mx,jonnylamb/mx,jonnylamb/mx,clutter-project/mx,pwithnall/mx,clutter-project/mx