src: fix accessing empty string

PR-URL: #57014
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Ulises Gascón <ulisesgascongonzalez@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

src/node_dotenv.cc

@@ -156,7 +156,7 @@ void Dotenv::ParseContent(const std::string_view input) {
     key = trim_spaces(key);
 
     // If the value is not present (e.g. KEY=) set is to an empty string
-    if (content.front() == '\n') {
+    if (content.empty() || content.front() == '\n') {
       store_.insert_or_assign(std::string(key), "");
       continue;
     }