[pygobject] tests: Fix failure due to new GTK+ warning regarding size_allocate()

[Simon Feltman <sfeltman src gnome org>]

commit 4164e7088be446fcab65cef642c6853aad3b6a69
Author: Simon Feltman <sfeltman src gnome org>
Date:   Sat Oct 31 14:06:40 2015 -0700

    tests: Fix failure due to new GTK+ warning regarding size_allocate()
    
    Call get_preferred_size() to avoid size_allocated() warning in
    size-allocated signal handler test.

 tests/test_overrides_gtk.py |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/tests/test_overrides_gtk.py b/tests/test_overrides_gtk.py
index 44f2f6e..9aa592c 100644
--- a/tests/test_overrides_gtk.py
+++ b/tests/test_overrides_gtk.py
@@ -692,6 +692,7 @@ class TestSignals(unittest.TestCase):
 
         with realized(win):
             win.show()
+            win.get_preferred_size()
             win.size_allocate(rect)
             self.assertTrue(win._alloc_called)
             self.assertIsInstance(win._alloc_value, Gdk.Rectangle)