Throw clean exception if query is not well formed (elastic#866)

Author: ebuildy

mr/src/main/java/org/elasticsearch/hadoop/rest/query/QueryUtils.java

@@ -42,6 +42,9 @@ public static QueryBuilder parseQuery(Settings settings) {
             try {
                 // must be a resource
                 InputStream in = settings.loadResource(query);
+                if (in == null) {
+                    throw new IOException();
+                }
                 query = IOUtils.asString(in);
             } catch (IOException ex) {
                 throw new EsHadoopIllegalArgumentException(
@@ -117,4 +120,4 @@ public static boolean isExplicitlyRequested(String candidate, String... indices)
         }
         return result;
     }
-}
+}