Fix possible realloc overflow for gpgsm and uiserver engines.

* src/engine-gpgsm.c (status_handler):
* src/engine-uiserver.c (status_handler):

After a realloc (realloc is also used for initial alloc) the allocated
size if the buffer is not correctly recorded. Thus an overflow can be
introduced by receiving data with different line lengths in a specific
order. This is not easy exploitable because libassuan constructs the
line. However a crash has been reported and thus it might be possible
to constructs an exploit.

CVE-id: CVE-2014-3564

• Reported-by: Tomáš Trnka