fix crash when enum has invalid field
fix crash when enum has invalid field

closes #468

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