add regression test for already fixed bug

closes #3586

Author: andrewrk

test/stage1/behavior.zig

@@ -38,6 +38,7 @@ comptime {
     _ = @import("behavior/bugs/3112.zig");
     _ = @import("behavior/bugs/3367.zig");
     _ = @import("behavior/bugs/3384.zig");
+    _ = @import("behavior/bugs/3586.zig");
     _ = @import("behavior/bugs/3742.zig");
     _ = @import("behavior/bugs/394.zig");
     _ = @import("behavior/bugs/421.zig");

test/stage1/behavior/bugs/3586.zig

@@ -0,0 +1,11 @@
+const NoteParams = struct {};
+
+const Container = struct {
+    params: ?NoteParams,
+};
+
+test "fixed" {
+    var ctr = Container{
+        .params = NoteParams{},
+    };
+}