AstGen yet another switch result loc bug

[Vexu]

test {
    const S = struct {
        fn foo() !u8 {
            return error.Foo;
        }
    };
    const value = S.foo() catch |err| switch (err) {
        error.Foo => 255,
    };
    try expect(value == 255);
}

a.zig:14:39: error: value with comptime only type 'comptime_int' depends on runtime control flow
    const value = S.foo() catch |err| switch (err) {
                                      ^
a.zig:14:47: note: runtime control flow here
    const value = S.foo() catch |err| switch (err) {
                                              ^

[andrewrk]

fixed by acca16c