Leading minus signs throw ArgumentOutOfRangeException

[henryfailbetter]

Hi, I had a problem with the parser where expressions with leading minus signs threw an out of range exception. Apologies if this format is not supported.

The expression in question was "-(3+2+1+6)/4".

System.ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection. Parameter name: index at System.ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument argument, ExceptionResource resource) at System.Collections.Generic.List1.get_Item(Int32 index) at Mathos.Parser.MathParser.BasicArithmeticalExpression(List1 tokens) at Mathos.Parser.MathParser.MathParserLogic(List1 tokens) at Mathos.Parser.MathParser.Parse(String mathExpression) at ...

[napen123]

This should be fixed by #23 (courtesy of @dennisvg111).