fix sheet regeneration missing drawing Identifier

Was passing LAYOUT document reference to sheeter instead of
DRAWING document reference

src/blenderbim/blenderbim/tool/drawing.py

@@ -251,17 +251,16 @@ def create_svg_sheet(cls, document, titleblock):
     def add_drawings(cls, sheet):
         sheet_builder = sheeter.SheetBuilder()
         sheet_builder.data_dir = bpy.context.scene.BIMProperties.data_dir
-        sheet_reference = None
+        drawing_references = {}
         drawing_names = []
         for reference in cls.get_document_references(sheet):
             reference_description = cls.get_reference_description(reference)
-            if reference_description == "LAYOUT":
-                sheet_reference = reference
-            elif reference_description == "DRAWING":
+            if reference_description == "DRAWING":
+                drawing_references[Path(reference.Location).stem] = reference
                 drawing_names.append(Path(reference.Location).stem)
-        for annotation in [e for e in tool.Ifc.get().by_type("IfcAnnotation") if e.ObjectType == "DRAWING"]:
-            if annotation.Name in drawing_names:
-                sheet_builder.add_drawing(sheet_reference, annotation, sheet)
+        for drawing_annotation in [e for e in tool.Ifc.get().by_type("IfcAnnotation") if e.ObjectType == "DRAWING"]:
+            if drawing_annotation.Name in drawing_names:
+                sheet_builder.add_drawing(drawing_references[drawing_annotation.Name], drawing_annotation, sheet)
 
     @classmethod
     def delete_collection(cls, collection):