Security update for MozillaThunderbird

This update for MozillaThunderbird to version 52.6 fixes several issues. These security issues were fixed: - CVE-2018-5095: Integer overflow in Skia library during edge builder allocation (bsc#1077291). - CVE-2018-5096: Use-after-free while editing form elements (bsc#1077291). - CVE-2018-5097: Use-after-free when source document is manipulated during XSLT (bsc#1077291). - CVE-2018-5098: Use-after-free while manipulating form input elements (bsc#1077291). - CVE-2018-5099: Use-after-free with widget listener (bsc#1077291). - CVE-2018-5102: Use-after-free in HTML media elements (bsc#1077291). - CVE-2018-5103: Use-after-free during mouse event handling (bsc#1077291). - CVE-2018-5104: Use-after-free during font face manipulation (bsc#1077291). - CVE-2018-5117: URL spoofing with right-to-left text aligned left-to-right (bsc#1077291). - CVE-2018-5089: Various memory safety bugs (bsc#1077291). These security issues were fixed: - Searching message bodies of messages in local folders, including filter and quick filter operations, not working reliably: Content not found in base64-encode message parts, non-ASCII text not found and false positives found. - Defective messages (without at least one expected header) not shown in IMAP folders but shown on mobile devices - Calendar: Unintended task deletion if numlock is enabled