wmaker: avoid allocating temporary memory in GetShortcutKey (Coverity #50115)
As pointed by Coverity, the function GetShortcutKey was allocating memory
for temporary operation, and did not free it in the end.
Because it participates in memory fragmentation and it is not really
efficient, this patch removes the allocation and uses a local storage on
the stack, and replaces wstrappend in favour of a fast string build.
Signed-off-by: Christophe CURIS <christophe.curis@free.fr>
Signed-off-by: Carlos R. Mafra <crmafra@gmail.com>