fix(preferences(mail)): make sure auto-reply (vacation) text is set

SoObjects/SOGo/SOGoSieveManager.m

@@ -964,6 +964,9 @@ static NSString *sieveScriptName = @"sogo";
       text = [values objectForKey: @"autoReplyText"];
       b = YES;
 
+      if (!text)
+        text = @"";
+
       if (!useCustomSubject)
         {
           // If user has not specified a custom subject, fallback to the domain's defaults

UI/Templates/PreferencesUI/UIxPreferences.wox

@@ -985,6 +985,7 @@
                   </var:if>
                   <textarea name="autoReplyText"
                             id="autoReplyText"
+                            ng-required="app.preferences.defaults.Vacation.enabled == 1"
                             ng-model="app.preferences.defaults.Vacation.autoReplyText"/>
                   <var:if condition="vacationFooter.length">
                     <p class="text-preview" md-colors="::{color: 'default-background-600'}"><var:string value="vacationFooter"/></p>