Dereferencing possibly NULL "str" in call to function "memcpy" (Deref assumed on the basis of 'nonnull' parameter attribute.)

If _XkbGetReadBufferPtr returns NULL, goto BAILOUT
Reviewed-by: Dirk Wallenstein <halsmit@t-online.de>
Reviewed-by: Ander Conselvan de Oliveira <ander.conselvan-de-oliveira@nokia.com>
Signed-off-by: Erkki Seppälä <erkki.seppala@vincit.fi>
Backported-to-NX-by: Ulrich Sibiller <uli42@gmx.de>