Fix missing return statement in embed_win32.cpp

Author: mfisher31

src/embed_win32.cpp

@@ -13,7 +13,7 @@ class HWNDEmbed : public detail::Embed {
     HWNDEmbed (lui::Embed& o) : detail::Embed (o) {}
     ~HWNDEmbed() = default;
 
-    void* native_view() const noexcept { nullptr; }
+    void* native_view() const noexcept { return nullptr; }
 
     void view_changed() {
         if (attachment == nullptr)