drivers/syslog: Avoid prepending process name when no TCB is available

Signed-off-by: Gustavo Henrique Nihei <gustavo.nihei@espressif.com>

drivers/syslog/vsyslog.c

@@ -206,7 +206,8 @@ int nx_vsyslog(int priority, FAR const IPTR char *fmt, FAR va_list *ap)
   /* Prepend the process name */
 
   tcb = nxsched_get_tcb(getpid());
-  ret += lib_sprintf(&stream.public, "%s: ", tcb->name);
+  ret += lib_sprintf(&stream.public, "%s: ",
+                     (tcb != NULL) ? tcb->name : "(null)");
 #endif
 
   /* Generate the output */