Explicitly mark the result of detail::names as constexpr

It might make no sense, but on MSVC it can generate a compile-time
error, especially if an enumerator's value is out of range.

Example:
error C3615: constexpr function 'magic_enum::detail::names' cannot
result in a constant expression
...
note: failure was caused by call of undefined function or one not
declared 'constexpr'
...
note: see usage of '__builtin_array_init_helper'

include/magic_enum.hpp

@@ -827,7 +827,8 @@ inline constexpr auto max_v = (count_v<E, S> > 0) ? static_cast<U>(values_v<E, S
 
 template <typename E, enum_subtype S, std::size_t... I>
 constexpr auto names(std::index_sequence<I...>) noexcept {
-  return std::array<string_view, sizeof...(I)>{{enum_name_v<E, values_v<E, S>[I]>...}};
+    constexpr auto result = std::array<string_view, sizeof...(I)>{{enum_name_v<E, values_v<E, S>[I]>...}};
+    return result;
 }
 
 template <typename E, enum_subtype S>

test/test.cpp

@@ -510,6 +510,11 @@ class a_foo2 {
 };
 } // namespace
 
+enum class LargeNumbers {
+    First = -1024,
+    Second = 1024
+};
+
 TEST_CASE("enum_name") {
   SECTION("automatic storage") {
     constexpr Color cr = Color::RED;
@@ -646,6 +651,13 @@ TEST_CASE("enum_name") {
     REQUIRE(enum_name<Binary::ONE>() == "ONE");
     REQUIRE(enum_name<MaxUsedAsInvalid::ONE>() == "ONE");
   }
+
+  SECTION("empty if the value is out of range") {
+    const auto ln_value = GENERATE(LargeNumbers::First, LargeNumbers::Second);
+    const auto ln_name = enum_name(ln_value);
+
+    REQUIRE(ln_name.empty());
+  }
 }
 
 TEST_CASE("enum_names") {