Run price & earnings through utf8_encode

This fixes the following notices -

Notice: iconv() [function.iconv]: Detected an illegal character in input string in /wp-content/plugins/easy-digital-downloads/includes/admin/reporting/pdf-reports.php on line 113

Notice: iconv() [function.iconv]: Detected an illegal character in input string in /wp-content/plugins/easy-digital-downloads/includes/admin/reporting/pdf-reports.php on line 114
Merge pull request #2266 from elliott-stocks/patch-22

Run price & earnings through utf8_encode