Fix error if no ifc file set (#1620)

* Fix error trying to access unset ifc file

* Return prematurely from operator if no file is set

* Revert "Return prematurely from operator if no file is set"

This reverts commit f876cfbcef.

* Revert "Fix error trying to access unset ifc file"

This reverts commit 6782c47d86.

* Prevent error message if ifc_types enum is empty

* Hide panel if no ifc file to avoid error

src/blenderbim/blenderbim/bim/module/model/ui.py

@@ -9,6 +9,10 @@ class BIM_PT_authoring(Panel):
     bl_region_type = "UI"
     bl_category = "BlenderBIM"
 
+    @classmethod
+    def poll(cls, context):
+        return IfcStore.get_file()
+
     def draw(self, context):
         tprops = context.scene.BIMTypeProperties
         col = self.layout.column(align=True)

src/blenderbim/blenderbim/bim/module/type/prop.py

@@ -42,7 +42,7 @@ def getIfcTypes(self, context):
 
 def getAvailableTypes(self, context):
     global available_types_enum
-    if len(available_types_enum) < 1:
+    if len(available_types_enum) < 1 and getIfcTypes(self, context):
         elements = IfcStore.get_file().by_type(self.ifc_class)
         available_types_enum.extend((str(e.id()), e.Name, "") for e in elements)
     return available_types_enum