refactor: tweak the horrible code in SearchableField (ietf-tools#3957)

* Fix: Tweak the horrible code in SearchableField so another corner case works

Fixes ietf-tools#3940. Hopefully doesn't break anything.

* fix: remove incorrect remaining loop.

Co-authored-by: Robert Sparks <rjsparks@nostrum.com>

Author: larseggert

ietf/utils/fields.py

@@ -264,10 +264,7 @@ def prepare_value(self, value):
                 value = value[0]
             else:
                 if not isinstance(value[0], self.model):
-                    qs = self.get_model_instances(value[0])
-                    for val in value[1:]:
-                        qs = qs.union(self.get_model_instances(val))
-                    value = qs
+                    value = self.get_model_instances(value)
         if isinstance(value, int):
             value = str(value)
         if isinstance(value, str):
@@ -343,4 +340,4 @@ def update_dimension_fields(self, *args, **kwargs):
         try:
             super().update_dimension_fields(*args, **kwargs)
         except FileNotFoundError:
-            pass  # don't do anything if the file has gone missing
+            pass  # don't do anything if the file has gone missing