zlib: fix crash when initializing failed

Unset `mode_` when initializing the zlib stream failed, so that
we don’t try to call the zlib end functions (`deflateEnd()` etc.)
when cleaning up in `ZCtx::Close()`.

Fixes: nodejs#14178
Ref: nodejs#13098

src/node_zlib.cc

@@ -557,6 +557,7 @@ class ZCtx : public AsyncWrap {
         delete[] dictionary;
         ctx->dictionary_ = nullptr;
       }
+      ctx->mode_ = NONE;
       ctx->env()->ThrowError("Init error");
     }