<AWT Dev> RFR: 8155772: gtk3_interface.c compilation error on Ubuntu 12.10

[Phil Race]

Bug : https://bugs.openjdk.java.net/browse/JDK-8155772

On my system in this file it appears NULL is "#define (void*)0 which 
causes the error

"error: initialization makes integer from pointer without a cast [-Werror]"

Webrev to fix in-line below.

-phil.

diff --git 
a/src/java.desktop/unix/native/libawt_xawt/awt/gtk3_interface.c 
b/src/java.desktop/unix/native/libawt_xawt/awt/gtk3_interface.c
--- a/src/java.desktop/unix/native/libawt_xawt/awt/gtk3_interface.c
+++ b/src/java.desktop/unix/native/libawt_xawt/awt/gtk3_interface.c
@@ -2547,14 +2547,14 @@

  static jobject get_integer_property(JNIEnv *env, GtkSettings* settings,
                                                               const 
gchar* key) {
-    gint intval = NULL;
+    gint intval = 0;
      (*fp_g_object_get)(settings, key, &intval, NULL);
      return create_Integer(env, intval);
  }

  static jobject get_boolean_property(JNIEnv *env, GtkSettings* settings,
                                                               const 
gchar* key) {
-    gint intval = NULL;
+    gint intval = 0;
      (*fp_g_object_get)(settings, key, &intval, NULL);
      return create_Boolean(env, intval);
  }