Add check to prevent substring going beyond string.

src/main/kotlin/ch/memobase/helpers/DateFacetBuildHelpers.kt

@@ -55,6 +55,10 @@ object DateFacetBuildHelpers {
      * @return The facet values used by outermedia.
      */
     fun buildFromNormalizedDateRange(date: String): List<String> {
+        if (date.length <= 3) {
+            log.error("Normalized date range has less than 4 characters: $date.")
+            return emptyList()
+        }
         val from = date.substring(0, 4)
         val until = if (date.contains("/")) {
             val secondPart = date.split("/")[1]