SAML2: Fix generation of mdui:Logo element with ampersand in URL.
SAML2: Fix generation of mdui:Logo element with ampersand in URL.

Thanks to Dick Visser for reporting this bug!
tectronics/simplesamlphp,tectronics/simplesamlphp,tectronics/simplesamlphp,vivekrajenderan/simplesamlphp,vivekrajenderan/simplesamlphp,vivekrajenderan/simplesamlphp,tectronics/simplesamlphp,tectronics/simplesamlphp,vivekrajenderan/simplesamlphp,vivekrajenderan/simplesamlphp