lib/xz: fix XZ_DYNALLOC to avoid useless memory reallocations

lib/xz: fix XZ_DYNALLOC to avoid useless memory reallocations

s->dict.allocated was initialized to 0 but never set after a successful
allocation, thus the code always thought that the dictionary buffer has
to be reallocated.

Link: http://lkml.kernel.org/r/20191104185107.3b6330df@tukaani.org
Signed-off-by: Lasse Collin <lasse.collin@tukaani.org>
Reported-by: Yu Sun <yusun2@cisco.com>
Acked-by: Daniel Walker <danielwa@cisco.com>
Cc: "Yixia Si (yisi)" <yisi@cisco.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>