TASK: Add '?' only if needed

[bstrilziw]

Takes care of #77

[mhsdesign]

Hi thank you:)

this is a regression from #28 - which complained that the space being encoded to + will not show up correct in the mail app.

I suggest to use the following snippet so spaces are correctly encoded as %20 via encodeURIComponent

convertModelToLink: (email:MailToLinkModel) => {
    const query = Object.entries({
            subject: email.subject,
            cc: email.cc,
            bcc: email.bcc,
            body: email.body,
        })
        .filter(([_key, value]) => value != null)
        .map(([key, value]) => `${key}=${encodeURIComponent(value as string)}`)
        .join('&');

    const href = `mailto:${email.recipient}${query ? `?${query}` : ''}`;

    return {href};
},

btw in the version which will be part of Neos 9.1 i already did this