LANG-1234: getLevenshteinDistance with a threshold: optimize implementation if the strings lengths differ more than the threshold (closes #118)

If the string lengths differ more than the threshold, there's no need for the algorithm to begin allocating arrays etc.

src/main/java/org/apache/commons/lang3/StringUtils.java

@@ -7585,6 +7585,10 @@ distance is O(nm), but a bound of k allows us to reduce it to O(km) time by only
         } else if (m == 0) {
             return n <= threshold ? n : -1;
         }
+        // no need to calculate the distance if the length difference is greater than the threshold
+        else if (Math.abs(n - m) > threshold) {
+            return -1;
+        }
 
         if (n > m) {
             // swap the two strings to consume less memory