Make RestUtils.decodeQueryString() more robust in edge cases

The code of decodeQueryString() had some trouble with weird URLs:

(1) an input like "uri?param&p=v" causes an exception to be thrown
(2) an input like "uri?param1&param2" causes an infinite loop

This could be verified against an ES server with requests like

    curl -XGET localhost:9200/test/_analyze?t&text=this+is+a+test
    # the exception stack trace shows up in logs

    curl -XGET localhost:9200/test/_analyze?t1&t2&text=this+is+a+test
    # never returns, never ends

This change fixes these issues.

Author: Adriano Ferreira

modules/elasticsearch/src/main/java/org/elasticsearch/rest/support/RestUtils.java

@@ -39,10 +39,9 @@ public static void decodeQueryString(String queryString, int fromIndex, Map<Stri
         int toIndex;
         while ((toIndex = queryString.indexOf('&', fromIndex)) >= 0) {
             int idx = queryString.indexOf('=', fromIndex);
-            if (idx < 0) {
-                continue;
+            if (fromIndex < idx && idx < toIndex) {
+                params.put(decodeComponent(queryString.substring(fromIndex, idx)), decodeComponent(queryString.substring(idx + 1, toIndex)));
             }
-            params.put(decodeComponent(queryString.substring(fromIndex, idx)), decodeComponent(queryString.substring(idx + 1, toIndex)));
             fromIndex = toIndex + 1;
         }
         int idx = queryString.indexOf('=', fromIndex);