[BUGFIX] Don't try to render icon for empty identifier

In case a site is missing a proper site
configuration - having no default language
a fallback SiteLanguage object is used in
the page module. This fallback however does
provide an empty string as flag identifier,
which does no longer result in a broken icon.

Resolves: #100799
Releases: main, 12.4, 11.5
Change-Id: I23f3d9347d2ea8a63520086054b9fa842a9f5cfd
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/78945


Reviewed-by: Nikita Hovratov <nikita.h@live.de>
Tested-by: Nikita Hovratov <nikita.h@live.de>
Tested-by: core-ci <typo3@b13.com>

typo3/sysext/backend/Resources/Private/Partials/PageLayout/RecordDefault/Header.html

 <div class="t3-page-ce-header row m-0 g-0 {f:if(condition: '{allowEditContent} && {item.dragAndDropAllowed}', then: 't3-page-ce-header-draggable t3js-page-ce-draghandle')}">
     <div class="col t3-page-ce-header-icons-left">
         {item.icons -> f:format.raw()}
-        <span class="t3js-flag" title="{item.siteLanguage.title}"><core:icon identifier="{item.siteLanguage.flagIdentifier}" /></span>
+        <f:if condition="{item.siteLanguage.flagIdentifier}">
+            <span class="t3js-flag" title="{item.siteLanguage.title}">
+                <core:icon identifier="{item.siteLanguage.flagIdentifier}" />
+            </span>
+        </f:if>
     </div>
     <div class="col-auto align-self-end t3-page-ce-header-icons-right">
         <f:if condition="{item.editable} && {allowEditContent}">