PATH: Prevent Job creation without Base object.

PathMillFace won't add a base if it isn't known to the parent

src/Mod/Path/PathScripts/PathJob.py

@@ -243,6 +243,9 @@ class TaskPanel:
         self.postProcessorArgsDefaultTooltip = self.form.cboPostProcessorArgs.toolTip()
 
     def accept(self):
+        if self.obj.Base is None:
+            QtGui.QMessageBox.information(None,"","No Base Object Selected.")
+            return
         self.getFields()
         FreeCADGui.ActiveDocument.resetEdit()
         FreeCADGui.Control.closeDialog()