SLING-7884 - Sanitize output of appender names

Closes #1
diff --git a/src/main/java/org/apache/sling/commons/log/logback/internal/SlingLogPanel.java b/src/main/java/org/apache/sling/commons/log/logback/internal/SlingLogPanel.java
index df83601..ac0004b 100644
--- a/src/main/java/org/apache/sling/commons/log/logback/internal/SlingLogPanel.java
+++ b/src/main/java/org/apache/sling/commons/log/logback/internal/SlingLogPanel.java
@@ -572,7 +572,7 @@
                 return;
             }
         }
-        pw.printf("No appender with name [%s] found", appenderName);
+        pw.printf("No appender with name [%s] found", XmlUtil.escapeXml(appenderName));
     }
 
     private String getLinkedName(FileAppender<ILoggingEvent> appender) throws UnsupportedEncodingException {