Bug when trying to upcast a delegate return type

[israellot]

var interpreter = new Interpreter().SetVariable("a", 123L);  
var del = interpreter.ParseAsDelegate<Func<object>>("a*2");

var interpreter = new Interpreter().SetVariable("a", 123L);  
var del = interpreter.ParseAsDelegate<Func<dynamic>>("a*2");

These simple examples used to run just fine on 2.8X and fails at 2.9.5.
I believe support to auto upcasting should be maintained.

[metoule]

Both examples worked with v2.8.1, but stopped working in v2.9.0, so it's linked to PR #140.
I'll investigate why it stopped working.

[metoule]

That was a side effect of the lambda expression support.

Background: the parser is able to correctly detect the type of an expression, but it emits a conversion expression from the actual type to the requested return type (so here, object).

When parsing a lambda expression, the return type is not known beforehand, so we use typeof(object) by default. That's an issue, because while the actual type was properly detected by the parser, it was lost due to a forced conversion to typeof(object). To prevent this, I no longer emitted the conversion expression if the return type was object, but that caused an issue if that's what's actually wanted!

To fix all this, when parsing a lambda expression, I now use typeof(void) to prevent the emission of the conversion expression.

[israellot]

Thanks @metoule ! I would go dig it myself and submit a PR later, but you were faster than me.