make rangeset_report_ranges() report all ranges

find_range() returns NULL when s is below the lowest range, so we have
to use first_range() here (which is as good performance wise).

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/common/rangeset.c
+++ b/xen/common/rangeset.c
@@ -289,7 +289,7 @@ int rangeset_report_ranges(
 
     read_lock(&r->lock);
 
-    for ( x = find_range(r, s); x && (x->s <= e) && !rc; x = next_range(r, x) )
+    for ( x = first_range(r); x && (x->s <= e) && !rc; x = next_range(r, x) )
         if ( x->e >= s )
             rc = cb(max(x->s, s), min(x->e, e), ctxt);