Add LCP check to fix toString in SuffixArray (#421)

When toString() was invoked just after creating the Suffix Array data structure, it gave null pointer exception when accessing actual array data member (sa) as the Suffix array and LCP array were not yet constructed.
Added a check to see if LCP was constructed before printing out the data members and construct them if needed.

Author: utpalsavliya

src/main/java/com/williamfiset/algorithms/datastructures/suffixarray/SuffixArray.java

@@ -88,6 +88,7 @@ private void kasai() {
 
   @Override
   public String toString() {
+    if (!constructedLcpArray) buildLcpArray();
     StringBuilder sb = new StringBuilder();
     sb.append("-----i-----SA-----LCP---Suffix\n");