[pygobject] Print exception if marshalling a signal argument fails

[Christoph Reiter <creiter src gnome org>]

commit e0b40099283a31ea23433f9d36dc9beebd4370c9
Author: Christoph Reiter <creiter src gnome org>
Date:   Mon Jun 6 11:34:47 2016 +0200

    Print exception if marshalling a signal argument fails
    
    For example if cairo support is missing a Gtk.Widget::draw call
    will result in
    "TypeError: Couldn't find foreign struct converter for 'cairo.Context'"
    
    https://bugzilla.gnome.org/show_bug.cgi?id=748198

 gi/pygi-signal-closure.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/gi/pygi-signal-closure.c b/gi/pygi-signal-closure.c
index bd9b402..f2698d5 100644
--- a/gi/pygi-signal-closure.c
+++ b/gi/pygi-signal-closure.c
@@ -181,6 +181,7 @@ pygi_signal_closure_marshal(GClosure *closure,
             }
 
             if (item == NULL) {
+                PyErr_Print ();
                 goto out;
             }
             PyTuple_SetItem(params, i, item);