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: #14178
Ref: #13098
PR-URL: #14666
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Alexey Orlenko <eaglexrlnk@gmail.com>

Author: addaleax

src/node_zlib.cc

@@ -562,6 +562,7 @@ class ZCtx : public AsyncWrap {
         delete[] dictionary;
         ctx->dictionary_ = nullptr;
       }
+      ctx->mode_ = NONE;
       ctx->env()->ThrowError("Init error");
     }
   }