Sema: fix unwrapping null when reporting error on member access

Closes #14399

Author: Vexu

src/Sema.zig

@@ -4643,11 +4643,11 @@ fn failWithBadMemberAccess(
         .Enum => "enum",
         else => unreachable,
     };
-    if (sema.mod.declIsRoot(agg_ty.getOwnerDecl())) {
+    if (agg_ty.getOwnerDeclOrNull()) |some| if (sema.mod.declIsRoot(some)) {
         return sema.fail(block, field_src, "root struct of file '{}' has no member named '{s}'", .{
             agg_ty.fmt(sema.mod), field_name,
         });
-    }
+    };
     const msg = msg: {
         const msg = try sema.errMsg(block, field_src, "{s} '{}' has no member named '{s}'", .{
             kw_name, agg_ty.fmt(sema.mod), field_name,

test/cases/compile_errors/bad_member_access_on_tuple.zig

@@ -0,0 +1,9 @@
+comptime {
+    _ = @TypeOf(.{}).is_optional;
+}
+
+// error
+// backend=stage2
+// target=native
+//
+// :2:21: error: struct '@TypeOf(.{})' has no member named 'is_optional'