src: guard against env != null in node_errors.cc

Otherwise
`TriggerUncaughtException()`
→ `PrintException()`
→ `GetErrorSource()`
can crash.

PR-URL: #36414
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Shelley Vohr <codebytere@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

src/node_errors.cc

@@ -63,7 +63,7 @@ static std::string GetErrorSource(Isolate* isolate,
   Environment* env = Environment::GetCurrent(isolate);
   const bool has_source_map_url =
       !message->GetScriptOrigin().SourceMapUrl().IsEmpty();
-  if (has_source_map_url && env->source_maps_enabled()) {
+  if (has_source_map_url && env != nullptr && env->source_maps_enabled()) {
     return sourceline;
   }