go/neo/proto: protogen: Fix it not to silently skip a pointer field

Without the fix any pointer field of a struct would be silently skipped
without any serialization code generated for it. With the patch default
case triggers in and reports detail where such type is and in which
struct/field it is used.

Besides *mem.Buf - that is handled specially - we don't have pointers in
proto.go, so this currently does not affect generated code at all.

Noticed accidentally.

go/neo/proto/protogen.go

-// Copyright (C) 2016-2020  Nexedi SA and Contributors.
+// Copyright (C) 2016-2021  Nexedi SA and Contributors.
 //                          Kirill Smelkov <kirr@nexedi.com>
 //
 // This program is free software: you can Use, Study, Modify and Redistribute
@@ -1241,8 +1241,6 @@ func codegenType(path string, typ types.Type, obj types.Object, codegen CodeGene
 	case *types.Map:
 		codegen.genMap(path, u, obj)
 
-	case *types.Pointer:
-
 	default:
 		log.Fatalf("%v: %v has unsupported type %v (%v)", pos(obj),
 			obj.Name(), typ, u)