entity: avoid using =default to avoid tricking VS toolset v141

src/entt/entity/registry.hpp

@@ -51,7 +51,8 @@ public:
     using difference_type = std::ptrdiff_t;
     using iterator_category = std::input_iterator_tag;
 
-    storage_proxy_iterator() ENTT_NOEXCEPT = default;
+    storage_proxy_iterator() ENTT_NOEXCEPT
+        : it{} {}
 
     storage_proxy_iterator(const It iter) ENTT_NOEXCEPT
         : it{iter} {}

src/entt/entity/runtime_view.hpp

@@ -37,7 +37,11 @@ public:
     using reference = typename iterator_type::reference;
     using iterator_category = std::bidirectional_iterator_tag;
 
-    runtime_view_iterator() ENTT_NOEXCEPT = default;
+    runtime_view_iterator() ENTT_NOEXCEPT
+        : pools{},
+          filter{},
+          it{},
+          tombstone_check{} {}
 
     runtime_view_iterator(const std::vector<const Type *> &cpools, const std::vector<const Type *> &ignore, iterator_type curr) ENTT_NOEXCEPT
         : pools{&cpools},

src/entt/entity/sparse_set.hpp

@@ -32,7 +32,9 @@ struct sparse_set_iterator final {
     using difference_type = typename Container::difference_type;
     using iterator_category = std::random_access_iterator_tag;
 
-    sparse_set_iterator() ENTT_NOEXCEPT = default;
+    sparse_set_iterator() ENTT_NOEXCEPT
+        : packed{},
+          offset{} {}
 
     sparse_set_iterator(const Container &ref, const difference_type idx) ENTT_NOEXCEPT
         : packed{std::addressof(ref)},