More constexpr fixes

tests/issues.cpp

@@ -0,0 +1,26 @@
+#include "catch.hpp"
+#include "expected.hpp"
+
+#include <string>
+
+using std::string;
+
+tl::expected<int, string> getInt3(int val)
+{
+    return val;
+}
+
+tl::expected<int, string> getInt2(int val)
+{
+    return val;
+}
+
+tl::expected<int, string> getInt1()
+{
+    return getInt2(5).and_then(getInt3);
+}
+
+
+TEST_CASE("Issue 1", "[issues.1]") {
+    getInt1();
+}