Fixed multiple select optgroup selected bug#276

hdwebpros wants to merge 2 commits intogetgrav:developgetgrav/grav-plugin-form:developfrom

hdwebpros:fix-select-optgroup-placeholder-and-multiple-selected-optionshdwebpros/grav-plugin-form:fix-select-optgroup-placeholder-and-multiple-selected-optionsCopy head branch name to clipboard