bonsai bcf - fix bim snippet ui issue

schema is optional field in bcf v2 and it was unreliable to use it to detect whether bim snippet is present or not

src/bonsai/bonsai/bim/module/bcf/prop.py

@@ -203,7 +203,7 @@ class BCFProperties(PropertyGroup):
     label: StringProperty(
         default="", name="Label", search=lambda s, c, t: get_extensions_items(s, c, t, extensions_attr="topic_labels")
     )
-    bim_snippet_reference: StringProperty(default="", name="Reference")
+    bim_snippet_reference: StringProperty(default="", name="Reference", description="URI or filepath to BimSnippet")
     bim_snippet_type: StringProperty(
         default="", name="Type", search=lambda s, c, t: get_extensions_items(s, c, t, extensions_attr="snippet_types")
     )

src/bonsai/bonsai/bim/module/bcf/ui.py

@@ -203,7 +203,7 @@ class BIM_PT_bcf_metadata(Panel):
         row.operator("bim.add_bcf_label")
 
         layout.label(text="BIM Snippet:")
-        if topic.bim_snippet.schema:
+        if topic.bim_snippet.reference:
             row = layout.row(align=True)
             row.prop(topic.bim_snippet, "type", emboss=False)
             if topic.bim_snippet.schema: