src: fix bug in GetErrorSource()

Refs: nodejs#43875

PR-URL: nodejs#44019
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Richard Lau <rlau@redhat.com>
Reviewed-By: Chengzhong Wu <legendecas@gmail.com>
Reviewed-By: Feng Yu <F3n67u@outlook.com>

src/node_errors.cc

@@ -105,7 +105,7 @@ static std::string GetErrorSource(Isolate* isolate,
   if (has_source_map_url && env != nullptr && env->source_maps_enabled()) {
     std::string source = GetSourceMapErrorSource(
         isolate, context, message, added_exception_line);
-    return added_exception_line ? source : sourceline;
+    return *added_exception_line ? source : sourceline;
   }
 
   // Because of how node modules work, all scripts are wrapped with a