Fixed the Center call for Shape objects on rotateAboutCenter, and changed CenterOfMass usage so that it won't fail silently.

cadquery/CQ.py

@@ -685,7 +685,8 @@ class CQ(object):
         endVec = Vector(axisEndPoint)
 
         def _rot(obj):
-            startPt = obj.Center()
+            # TODO: compute the weighted average instead of using the first solid
+            startPt = obj.Solids()[0].Center()
             endPt = startPt + endVec
             return obj.rotate(startPt, endPt, angleDegrees)
 

cadquery/freecad_impl/shapes.py

@@ -185,10 +185,10 @@ class Shape(object):
         return BoundBox(self.wrapped.BoundBox)
 
     def Center(self):
-        try:
-            return Vector(self.wrapped.CenterOfMass)
-        except:
-            pass
+        # try:
+        return Vector(self.wrapped.CenterOfMass)
+        # except:
+        #     pass
 
     def Closed(self):
         return self.wrapped.Closed