Comment 4 for bug 959570

StacktraceTop:
 __assert_fail_base (fmt=<optimized out>, assertion=0x7f92c05365b0 "((*&(&surface->ref_count)->ref_count) > 0)", file=0x7f92c0536580 "/build/buildd/cairo-1.10.2/src/cairo-surface.c", line=<optimized out>, function=<optimized out>) at assert.c:94
 __GI___assert_fail (assertion=0x7f92c05365b0 "((*&(&surface->ref_count)->ref_count) > 0)", file=0x7f92c0536580 "/build/buildd/cairo-1.10.2/src/cairo-surface.c", line=614, function=0x7f92c0536940 "cairo_surface_reference") at assert.c:103
 cairo_surface_reference (surface=<optimized out>) at /build/buildd/cairo-1.10.2/src/cairo-surface.c:614
 cairo_surface_reference (surface=<optimized out>) at /build/buildd/cairo-1.10.2/src/cairo-surface.c:608
 ?? ()