add test for struct with invalid field
add test for struct with invalid field

see #468

zig-lang/zig,Dimenus/zig,zig-lang/zig,Dimenus/zig,raulgrell/zig,zig-lang/zig,Dimenus/zig,andrewrk/zig,raulgrell/zig,raulgrell/zig,raulgrell/zig,raulgrell/zig,andrewrk/zig