fix: Use older logic to set module_name and custom vars

(cherry picked from commit 87ed7796de)

frappe/model/base_document.py

@@ -34,15 +34,9 @@ def get_controller(doctype):
 		from frappe.model.document import Document
 		from frappe.utils.nestedset import NestedSet
 
-		if frappe.flags.in_migrate or frappe.flags.in_install or frappe.flags.in_patch:
-			module_name, custom = ["Core", False]
-		else:
-			# this could be simplified in PY3.8 using walrus operators
-			result = frappe.db.get_value("DocType", doctype, ("module", "custom"), cache=True)
-			if result:
-				module_name, custom = result
-			else:
-				module_name, custom = ["Core", bool(not frappe.db.exists(doctype))]
+		module_name, custom = frappe.db.get_value(
+			"DocType", doctype, ("module", "custom"), cache=True
+		) or ["Core", False]
 
 		if custom:
 			if frappe.db.field_exists("DocType", "is_tree"):