[TASK] Small backend fixes when no extensions registered

Resources/Private/Language/de.locallang.xlf

@@ -189,6 +189,10 @@
 			<source>No template was registered.</source>
 			<target>Es wurde noch kein Template registriert.</target>
 		</trans-unit>
+		<trans-unit id="backend.no_extensions" approved="yes">
+			<source>No extensions registered</source>
+			<target>Es wurden noch keine Extensions registriert</target>
+		</trans-unit>
 		<trans-unit id="backend.no_queue_entries" approved="yes">
 			<source>Your filter criteria didn't match any entries.</source>
 			<target>Es wurden keine Einträge für Ihre Filtereinstellungen gefunden.</target>

Resources/Private/Language/locallang.xlf

@@ -144,6 +144,9 @@
 		<trans-unit id="backend.no_extension">
 			<source>No template was registered.</source>
 		</trans-unit>
+		<trans-unit id="backend.no_extensions">
+			<source>No extensions registered</source>
+		</trans-unit>
 		<trans-unit id="backend.no_queue_entries">
 			<source>Your filter criteria didn't match any entries.</source>
 		</trans-unit>

Resources/Private/Layouts/Empty.html

+{namespace sgm=SGalinski\SgMail\ViewHelpers}
+<f:be.container>
+	<div id="typo3-docbody">
+		<div id="typo3-inner-docbody">
+			<f:render section="content" />
+		</div>
+	</div>
+</f:be.container>

Resources/Private/Templates/Mail/Empty.html

+<f:layout name="Empty" />
+
+<f:section name="content">
+	<div class="alert alert-warning">
+		{f:translate(key:'backend.no_extensions')}
+	</div>
+</f:section>