A few small bugfixes discovered from online users of openapi-changes

someone caused a panic, exposed an untested bug.

Signed-off-by: quobix <dave@quobix.com>

datamodel/low/extraction_functions.go

@@ -823,6 +823,9 @@ func AreEqual(l, r Hashable) bool {
 	if l == nil || r == nil {
 		return false
 	}
+	if reflect.ValueOf(l).IsNil() || reflect.ValueOf(r).IsNil() {
+		return false
+	}
 	return l.Hash() == r.Hash()
 }