deskutils/gsimplecal: Fix build with Clang 6

MainWindow.cpp:157:33: error: C-style cast from 'nullptr_t' to 'GtkAccelFlags' is not allowed
                                (GtkAccelFlags)NULL, closure);
                                ^~~~~~~~~~~~~~~~~~~

http://beefy12.nyi.freebsd.org/data/head-amd64-default/p479076_s338486/logs/errors/gsimplecal-2.1.log

PR:		230883
Submitted by:	tobik
Approved by:	lme (maintainer timeout, 2 weeks)

1 files changed, 15 insertions, 0 deletions

diff --git a/deskutils/gsimplecal/files/patch-src_MainWindow.cpp b/deskutils/gsimplecal/files/patch-src_MainWindow.cpp
new file mode 100644
index 000000000000..c971675dbfbf
--- /dev/null
+++ b/deskutils/gsimplecal/files/patch-src_MainWindow.cpp
@@ -0,0 +1,15 @@
+MainWindow.cpp:157:33: error: C-style cast from 'nullptr_t' to 'GtkAccelFlags' is not allowed
+                                (GtkAccelFlags)NULL, closure);
+                                ^~~~~~~~~~~~~~~~~~~
+
+--- src/MainWindow.cpp.orig	2018-08-25 04:31:20 UTC
++++ src/MainWindow.cpp
+@@ -154,7 +154,7 @@ MainWindow::MainWindow()
+         closure = g_cclosure_new(G_CALLBACK(keys[key].func), (gpointer)this, NULL);
+         gtk_accel_group_connect(accelerators, keys[key].key,
+                                 (GdkModifierType)keys[key].modifier,
+-                                (GtkAccelFlags)NULL, closure);
++                                (GtkAccelFlags)0, closure);
+         g_closure_unref(closure);
+     }
+