fuzz-handle_onion_message: variable 'daemon' is used uninitialized whenever 'if' condition is true

[fanquake]

Turned up in fuzzing infra:

 #10 479.9 tests/fuzz/fuzz-handle_onion_message.c:78:6: error: variable 'daemon' is used uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
#10 479.9    78 |         if (setjmp(fuzz_env) != 0)
#10 479.9       |             ^~~~~~~~~~~~~~~~~~~~~
#10 479.9 /usr/include/setjmp.h:49:21: note: expanded from macro 'setjmp'
#10 479.9    49 | #define setjmp(env)     _setjmp (env)
#10 479.9       |                         ^
#10 479.9 tests/fuzz/fuzz-handle_onion_message.c:104:6: note: uninitialized use occurs here
#10 479.9   104 |         if (daemon)
#10 479.9       |             ^~~~~~
#10 479.9 tests/fuzz/fuzz-handle_onion_message.c:78:2: note: remove the 'if' if its condition is always false
#10 479.9    78 |         if (setjmp(fuzz_env) != 0)
#10 479.9       |         ^~~~~~~~~~~~~~~~~~~~~~~~~~
#10 479.9    79 |                 goto cleanup;
#10 479.9       |                 ~~~~~~~~~~~~
#10 479.9 tests/fuzz/fuzz-handle_onion_message.c:81:23: note: initialize the variable 'daemon' to silence this warning
#10 479.9    81 |         struct daemon *daemon;
#10 479.9       |                              ^
#10 479.9       |                               = NULL
#10 479.9 1 error generated.
#10 479.9 make: *** [Makefile:332: tests/fuzz/fuzz-handle_onion_message.o] Error 1

cc @dergoegge