tls: add CHECK for impossible condition

Backport-PR-URL: #26951
PR-URL: #26843
Reviewed-By: Sam Roberts <[email protected]>
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: Minwoo Jung <[email protected]>
Reviewed-By: Ben Noordhuis <[email protected]>
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Tobias Nießen <[email protected]>
Reviewed-By: Ruben Bridgewater <[email protected]>

src/tls_wrap.cc

@@ -747,10 +747,10 @@ void TLSWrap::OnStreamRead(ssize_t nread, const uv_buf_t& buf) {
     return;
   }
 
-  if (ssl_ == nullptr) {
-    EmitRead(UV_EPROTO);
-    return;
-  }
+  // DestroySSL() is the only thing that un-sets ssl_, but that also removes
+  // this TLSWrap as a stream listener, so we should not receive OnStreamRead()
+  // calls anymore.
+  CHECK(ssl_);
 
   // Commit the amount of data actually read into the peeked/allocated buffer
   // from the underlying stream.