Fix zstd compression with digested ZstdDict

Author: Rogdham

Modules/_zstd/compressor.c

@@ -347,6 +347,7 @@ _zstd_ZstdCompressor_new_impl(PyTypeObject *type, PyObject *level,
     }
 
     self->use_multithread = 0;
+    self->compression_level = ZSTD_CLEVEL_DEFAULT;
     self->dict = NULL;
     self->lock = (PyMutex){0};