PartDesign: fix a couple of crashes
PartDesign: fix a couple of crashes

The first crash was reported here:
http://forum.freecadweb.org/viewtopic.php?f=20&t=11205&start=50#p91052

The second one accures then moving a feature from a body without solid
features.

bblacey/FreeCAD-MacOS-CI,Fat-Zer/FreeCAD_sf_master,timthelion/FreeCAD,chrisjaquet/FreeCAD,Fat-Zer/FreeCAD_sf_master,maurerpe/FreeCAD,bblacey/FreeCAD-MacOS-CI,usakhelo/FreeCAD,Fat-Zer/FreeCAD_sf_master,Fat-Zer/FreeCAD_sf_master,chrisjaquet/FreeCAD,chrisjaquet/FreeCAD,usakhelo/FreeCAD,usakhelo/FreeCAD,Fat-Zer/FreeCAD_sf_master,timthelion/FreeCAD,maurerpe/FreeCAD,maurerpe/FreeCAD,wood-galaxy/FreeCAD,timthelion/FreeCAD,timthelion/FreeCAD,usakhelo/FreeCAD,bblacey/FreeCAD-MacOS-CI,timthelion/FreeCAD,timthelion/FreeCAD,wood-galaxy/FreeCAD,chrisjaquet/FreeCAD,maurerpe/FreeCAD,bblacey/FreeCAD-MacOS-CI,wood-galaxy/FreeCAD,usakhelo/FreeCAD,wood-galaxy/FreeCAD,chrisjaquet/FreeCAD,chrisjaquet/FreeCAD,maurerpe/FreeCAD,usakhelo/FreeCAD,bblacey/FreeCAD-MacOS-CI,wood-galaxy/FreeCAD,bblacey/FreeCAD-MacOS-CI,wood-galaxy/FreeCAD,chrisjaquet/FreeCAD,bblacey/FreeCAD-MacOS-CI,usakhelo/FreeCAD