[gtk/tracing] Copy a fix from sysprof

[Matthias Clasen <matthiasc src gnome org>]

commit 15a5c14f637baf9d6093860aaaeaa5c86ba405f8
Author: Matthias Clasen <mclasen redhat com>
Date:   Thu May 17 11:51:01 2018 +0100

    Copy a fix from sysprof
    
    Eventually, we will use the static library.
    For now, copy the fix.

 gdk/capture/sp-capture-writer.c | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/gdk/capture/sp-capture-writer.c b/gdk/capture/sp-capture-writer.c
index c4a89d65a6..5f53379f87 100644
--- a/gdk/capture/sp-capture-writer.c
+++ b/gdk/capture/sp-capture-writer.c
@@ -1077,6 +1077,8 @@ sp_capture_writer_set_counters (SpCaptureWriter             *self,
   if (!set)
     return FALSE;
 
+  memset (set, 0, len);
+
   sp_capture_writer_frame_init (&set->frame,
                                 len,
                                 cpu,