Fix potential argv overflow in windows option parsing
Fix potential argv overflow in windows option parsing

When parsing options like -breakmnu foobar
we should check argc before gobbling the next argument...
Otherwise, we would access argv out of range.
If there is no next argument, option is invalid.

OpenSmalltalk/vm,OpenSmalltalk/vm,timfel/squeakvm,OpenSmalltalk/vm,timfel/squeakvm,timfel/squeakvm,timfel/squeakvm,timfel/squeakvm,OpenSmalltalk/vm,timfel/squeakvm,OpenSmalltalk/vm,OpenSmalltalk/vm,timfel/squeakvm,OpenSmalltalk/vm,OpenSmalltalk/vm,timfel/squeakvm