Fix leak of struct call_thread_fsm in call_function_by_hand_dummy.

Fix leak of struct call_thread_fsm in call_function_by_hand_dummy.

When the call does not complete, the call_thread_fsm allocated
by new_call_thread_fsm is not cleaned up and deleted, which causes
the following leak e.g. in gdb.base/callfuncs.exp:

==29263== 560 bytes in 7 blocks are definitely lost in loss record 2,833 of 3,341
==29263==    at 0x4C2E0BC: calloc (vg_replace_malloc.c:762)
==29263==    by 0x405110: xcalloc (common-utils.c:84)
==29263==    by 0x4E67EB: xcnew<call_thread_fsm> (poison.h:122)
==29263==    by 0x4E67EB: new_call_thread_fsm (infcall.c:516)
==29263==    by 0x4E67EB: call_function_by_hand_dummy(value*, type*, gdb::array_view<value*>, void (*)(void*, int), void*) (infcall.c:1154)
==29263==    by 0x4E784E: call_function_by_hand(value*, type*, gdb::array_view<value*>) (infcall.c:693)
==29263==    by 0x496111: eval_call(expression*, noside, int, value**, char const*, type*) [clone .isra.5] (eval.c:835)

Fix the leak by similarly doing cleanup/destroy when restoring
previous state machine.

Tested on debian/amd64, natively and under valgrind.

2019-01-02  Philippe Waroquiers  <philippe.waroquiers@skynet.be>

	* infcall.c (call_function_by_hand_dummy): cleanup/destroy sm
	 in case of call that did not complete.