Add zero-length array test

This should compile warning-free, since it is legal Java. Previously
an array_of expression with nil length yielded a warning, as would a WITH
based upon one.

Author: smowton

regression/cbmc-java/array2/test.class

@@ -0,0 +1,6 @@
+CORE
+test.class
+--function test.f --cover location
+\d+ of \d+ covered
+--
+^warning: ignoring

regression/cbmc-java/array2/test.desc

@@ -0,0 +1,16 @@
+public class test {
+
+  public void f(int unknown) {
+
+    int[] arr;
+    if(unknown > 0)
+      arr = new int[1];
+    else
+      arr = new int[0];
+
+    if(unknown > 0)
+      arr[0]=1;
+
+  }
+
+}