fix #23943 - patch by Famlam - allow negative values for substring to…

… count from the end of the string

git-svn-id: https://josm.openstreetmap.de/svn/trunk@19259 0c6e7542-c601-0410-84e7-c038aed88b3b

src/org/openstreetmap/josm/gui/mappaint/mapcss/Functions.java

@@ -1034,12 +1034,12 @@ public static String substring(String s, /* due to missing Cascade.convertTo for
      * and ending at index {@code end}, (exclusive, 0-indexed).
      * @param s The base string
      * @param begin The start index
-     * @param end The end index
+     * @param end The end index. If negative, it counts from the end of the string
      * @return the substring
      * @see String#substring(int, int)
      */
     public static String substring(String s, float begin, float end) {
-        return s == null ? null : s.substring((int) begin, (int) end);
+        return s == null ? null : s.substring((int) begin, (int) (end >= 0 ? end : s.length() + end));
     }
 
     /**