Fixed JNI call for hasNext() in requestResources.

Apparently a typical copy-paste mistake of the programmer of this
code. hasNext() was called on ArrayList instead of on iterator.

Review: https://reviews.apache.org/r/18976
diff --git a/src/java/jni/org_apache_mesos_MesosSchedulerDriver.cpp b/src/java/jni/org_apache_mesos_MesosSchedulerDriver.cpp
index d2369ac..d0b7152 100644
--- a/src/java/jni/org_apache_mesos_MesosSchedulerDriver.cpp
+++ b/src/java/jni/org_apache_mesos_MesosSchedulerDriver.cpp
@@ -904,7 +904,7 @@
 
   jmethodID next = env->GetMethodID(clazz, "next", "()Ljava/lang/Object;");
 
-  while (env->CallBooleanMethod(jrequests, hasNext)) {
+  while (env->CallBooleanMethod(jiterator, hasNext)) {
     // Object task = iterator.next();
     jobject jrequest = env->CallObjectMethod(jiterator, next);
     const Request& request = construct<Request>(env, jrequest);