LibWeb: Ensure requests modules is not empty before indexing into it

Regression from 5af613aa65

Fixes: #2676

Tests/LibWeb/Text/input/HTML/ModuleLoading/import-in-a-module.js

@@ -0,0 +1,5 @@
+// NOTE: Doesn't matter what this imports, but this imports itself so there is no import error in test logs.
+import("./import-in-a-module.js");
+
+const returnValue = "PASS! (Didn't crash)";
+export default returnValue;

Tests/LibWeb/Text/input/HTML/ModuleLoading/import-inside-of-a-module.html

@@ -0,0 +1,8 @@
+<script src="../../include.js"></script>
+<script type="module">
+    import m from "./import-in-a-module.js";
+
+    test(() => {
+        println(m);
+    });
+</script>