Alarm 'enabled state' NPE fix

enabled_date may be null, and alarm table checking value updates via
hash code would then run into NullPointerException

Author: kasemir

app/alarm/model/src/main/java/org/phoebus/applications/alarm/model/EnabledState.java

@@ -54,7 +54,7 @@ public int hashCode()
     {
         final int prime = 31;
         final int enabled_check = this.enabled ? 1 : 0;
-        int result = enabled_date.hashCode();
+        int result = enabled_date == null ? 0 : enabled_date.hashCode();
         result = prime * result + enabled_check;
         return result;
     }