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

Regression from 5af613aa65

Fixes: #2676

Libraries/LibWeb/Bindings/MainThreadVM.cpp

@@ -471,7 +471,9 @@ ErrorOr<void> initialize_main_thread_vm(HTML::EventLoop::Type type)
         }
 
         // 7. If referrer is a Cyclic Module Record and moduleRequest is equal to the first element of referrer.[[RequestedModules]], then:
-        if (referrer.has<GC::Ref<JS::CyclicModule>>() && module_request == referrer.get<GC::Ref<JS::CyclicModule>>()->requested_modules().first()) {
+        if (referrer.has<GC::Ref<JS::CyclicModule>>()) {
+            // FIXME: Why do we need to check requested modules is empty here?
+            if (auto const& requested_modules = referrer.get<GC::Ref<JS::CyclicModule>>()->requested_modules(); !requested_modules.is_empty() && module_request == requested_modules.first()) {
                 // 1. For each ModuleRequest record requested of referrer.[[RequestedModules]]:
                 for (auto const& module_request : referrer.get<GC::Ref<JS::CyclicModule>>()->requested_modules()) {
                     // 1. If moduleRequest.[[Attributes]] contains a Record entry such that entry.[[Key]] is not "type", then:
@@ -528,6 +530,7 @@ ErrorOr<void> initialize_main_thread_vm(HTML::EventLoop::Type type)
                 //            as one that cannot be parsed; in both cases, a syntactic issue makes it impossible to ever
                 //            contemplate linking the module later.
             }
+        }
 
         // 8. Disallow further import maps given moduleMapRealm.
         HTML::disallow_further_import_maps(*module_map_realm);

Tests/LibWeb/Text/expected/HTML/ModuleLoading/import-inside-of-a-module.txt

@@ -0,0 +1 @@
+PASS! (Didn't crash)

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>