Always restore serialization reader state after deserializing

We already did this for other deserialization types. This extends coverage to
objects and method caches as well, so it should now be safe to deserialize
anything without losing the reader's position.

src/6model/serialization.c

@@ -2812,6 +2812,10 @@ static void deserialize_object(MVMThreadContext *tc, MVMSerializationReader *rea
         /* Calculate location of object's table row. */
         char *obj_table_row = reader->root.objects_table + i * OBJECTS_TABLE_ENTRY_SIZE;
 
+        char     **orig_read_buffer         = reader->cur_read_buffer;
+        MVMint32  *orig_read_offset         = reader->cur_read_offset;
+        char     **orig_read_end            = reader->cur_read_end;
+
         /* Set current read buffer to the correct thing. */
         reader->cur_read_buffer = &(reader->root.objects_data);
         reader->cur_read_offset = &(reader->objects_data_offset);
@@ -2826,6 +2830,10 @@ static void deserialize_object(MVMThreadContext *tc, MVMSerializationReader *rea
             fail_deserialize(tc, NULL, reader, "Missing deserialize REPR function for %s (%s)",
                 REPR(obj)->name, MVM_6model_get_debug_name(tc, obj));
         reader->current_object = NULL;
+
+        reader->cur_read_buffer     = orig_read_buffer;
+        reader->cur_read_offset     = orig_read_offset;
+        reader->cur_read_end        = orig_read_end;
     }
 }
 
@@ -3018,6 +3026,10 @@ void MVM_serialization_finish_deserialize_method_cache(MVMThreadContext *tc, MVM
         if (st->method_cache_sc) {
             MVMObject *cache;
 
+            char     **orig_read_buffer         = sr->cur_read_buffer;
+            MVMint32  *orig_read_offset         = sr->cur_read_offset;
+            char     **orig_read_end            = sr->cur_read_end;
+
             /* Set reader's position. */
             sr->stables_data_offset    = st->method_cache_offset;
             sr->cur_read_buffer        = &(sr->root.stables_data);
@@ -3039,6 +3051,10 @@ void MVM_serialization_finish_deserialize_method_cache(MVMThreadContext *tc, MVM
             MVM_gc_allocate_gen2_default_clear(tc);
             sr->working--;
             st->method_cache_sc = NULL;
+
+            sr->cur_read_buffer     = orig_read_buffer;
+            sr->cur_read_offset     = orig_read_offset;
+            sr->cur_read_end        = orig_read_end;
         }
         MVM_reentrantmutex_unlock(tc, (MVMReentrantMutex *)sc->body->mutex);
     }