Updated parse_infix(..) in mysql.rs and sqlite.rs to handle error rather than unwrap()

[RPG-Alex]

Previously for both sqlite and mysql the parse_infix would panic if passed parser: &mut crate::parser::Parser returned an error:

    fn parse_infix(
        &self,
        parser: &mut crate::parser::Parser,
        expr: &crate::ast::Expr,
        _precedence: u8,
    ) -> Option<Result<crate::ast::Expr, ParserError>> {
        // Parse DIV as an operator
        if parser.parse_keyword(Keyword::DIV) {
            Some(Ok(Expr::BinaryOp {
                left: Box::new(expr.clone()),
                op: BinaryOperator::MyIntegerDivide,
                right: Box::new(parser.parse_expr().unwrap()),
            }))
        } else {
            None
        }
    }

Now Errors are being passed, and the parse_expr() error returned will be returned for parse_infix rather than panic:

    fn parse_infix(
        &self,
        parser: &mut crate::parser::Parser,
        expr: &crate::ast::Expr,
        _precedence: u8,
    ) -> Option<Result<crate::ast::Expr, ParserError>> {
        // Parse DIV as an operator
        if parser.parse_keyword(Keyword::DIV) {
            let left = Box::new(expr.clone());
            let right = Box::new(match parser.parse_expr() {
                Ok(expr) => expr,
                Err(e) => return Some(Err(e)),
            });
            Some(Ok(Expr::BinaryOp {
                left,
                op: BinaryOperator::MyIntegerDivide,
                right,
            }))
        } else {
            None
        }
    }

[RPG-Alex]

I realized the sqlite.rs parse_infix() was already patched. My PR only applies to mysql.rs now.