libxl: Do not use-after-free on ao progress reporting

We need to call libxl__free_all after egc_run_callbacks since some of
the callbacks might be ao progress reports allocated from the egc's
gc.

Fixes a segfault in egc_run_callbacks.

Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Committed-by: Ian Campbell <ian.campbell@citrix.com>

tools/libxl/libxl_event.c

@@ -988,9 +988,9 @@ static void egc_run_callbacks(libxl__egc *egc)
 void libxl__egc_cleanup(libxl__egc *egc)
 {
     EGC_GC;
-    libxl__free_all(gc);
-
     egc_run_callbacks(egc);
+
+    libxl__free_all(gc);
 }
 
 /*