Fix removing signature when switching to identity with an empty sig in HTML mode (#1490470)

CHANGELOG

@@ -34,6 +34,7 @@ CHANGELOG Roundcube Webmail
 - Fix wrong positioning of message list header on page scroll in Webkit browsers (#1490035)
 - Fix some javascript errors in rare situations (#1490441)
 - Fix error when using back button after sending an email (#1490009)
+- Fix removing signature when switching to identity with an empty sig in HTML mode (#1490470)
 
 RELEASE 1.1.2
 -------------

program/js/editor.js

@@ -548,9 +548,7 @@ function rcube_text_editor(config, id)
         }
       }
 
-      if (rcmail.env.signatures[id]) {
-        sigElem.innerHTML = rcmail.env.signatures[id].html;
-      }
+      sigElem.innerHTML = rcmail.env.signatures[id] ? rcmail.env.signatures[id].html : '';
     }
     else if (!rcmail.env.top_posting) {
       position_element = $(this.editor.getBody()).children().last();