journald: unitialized variable access

journald: unitialized variable access

../src/journal/journald-native.c:341:13: warning: variable 'context' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
        if (ucred && pid_is_valid(ucred->pid)) {
            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../src/journal/journald-native.c:350:42: note: uninitialized use occurs here
                                         context, ucred, tv, label, label_len);
                                         ^~~~~~~
../src/journal/journald-native.c:335:31: note: initialize the variable 'context' to silence this warning
        ClientContext *context;
                              ^
                               = NULL

Very nice reporting!

Functions that we call can handle context == NULL, so it's enough to simply
initialize the variable.