util: Make it possible for virResctrlAllocSetMask to replace existing mask

This wil be used in the future, but it makes sense for now as well.  It makes
sure there is no mask leftover that would leak.
Signed-off-by: NMartin Kletzander <mkletzan@redhat.com>

src/util/virresctrl.c

@@ -1239,6 +1239,7 @@ virResctrlAllocSetMask(virResctrlAllocPerTypePtr a_type,
                      cache - a_type->nmasks + 1) < 0)
         return -1;
 
+    virBitmapFree(a_type->masks[cache]);
     a_type->masks[cache] = mask;
 
     return 0;