[Windows] Fix headless mode crash (#38173)

Author: loic-sharma

shell/platform/windows/flutter_windows.cc

@@ -145,7 +145,12 @@ bool FlutterDesktopEngineDestroy(FlutterDesktopEngineRef engine_ref) {
 
 bool FlutterDesktopEngineRun(FlutterDesktopEngineRef engine,
                              const char* entry_point) {
-  return EngineFromHandle(engine)->Run(entry_point);
+  std::string_view entry_point_view{""};
+  if (entry_point != nullptr) {
+    entry_point_view = entry_point;
+  }
+
+  return EngineFromHandle(engine)->Run(entry_point_view);
 }
 
 uint64_t FlutterDesktopEngineProcessMessages(FlutterDesktopEngineRef engine) {

shell/platform/windows/flutter_windows_unittests.cc

@@ -89,6 +89,16 @@ TEST_F(WindowsTest, LaunchCustomEntrypointInEngineRunInvocation) {
   ASSERT_TRUE(FlutterDesktopEngineRun(engine.get(), "customEntrypoint"));
 }
 
+// Verify that the engine can launch in headless mode.
+TEST_F(WindowsTest, LaunchHeadlessEngine) {
+  auto& context = GetContext();
+  WindowsConfigBuilder builder(context);
+  EnginePtr engine{builder.InitializeEngine()};
+  ASSERT_NE(engine, nullptr);
+
+  ASSERT_TRUE(FlutterDesktopEngineRun(engine.get(), nullptr));
+}
+
 // Verify that engine fails to launch when a conflicting entrypoint in
 // FlutterDesktopEngineProperties.dart_entrypoint and the
 // FlutterDesktopEngineRun parameter.

shell/platform/windows/public/flutter_windows.h

@@ -147,7 +147,7 @@ FLUTTER_EXPORT bool FlutterDesktopEngineDestroy(FlutterDesktopEngineRef engine);
 // set in the dart_entrypoint field of the FlutterDesktopEngineProperties
 // struct passed to FlutterDesktopEngineCreate.
 //
-// If sprecified, entry_point must be the name of a top-level function from the
+// If specified, entry_point must be the name of a top-level function from the
 // same Dart library that contains the app's main() function, and must be
 // decorated with `@pragma(vm:entry-point)` to ensure the method is not
 // tree-shaken by the Dart compiler. If conflicting non-null values are passed