Prevent Loop in BRepBuilderAPI_Transform

- if a scale transform with scale = 0 is passed to
  BRepBuilderAPI_Transform, it will loop forever.
  If Page.keepUpdated is false, and Views have not yet
  been executed (ex at load time), Views will have a
  0.0 x 0.0 bbox and if Autoscale is true, a scale of
  0.0 will be used in fit-to-page.

src/Mod/TechDraw/App/DrawUtil.cpp

@@ -400,6 +400,9 @@ Base::Vector3d  DrawUtil::closestBasis(Base::Vector3d v)
 double DrawUtil::sensibleScale(double working_scale)
 {
     double result = 1.0;
+    if (!(working_scale > 0.0)) {
+        return result;
+    }
     //which gives the largest scale for which the min_space requirements can be met, but we want a 'sensible' scale, rather than 0.28457239...
     //eg if working_scale = 0.115, then we want to use 0.1, similarly 7.65 -> 5, and 76.5 -> 50