[MINOR] recompute maxfd before touching fdtab

It may be dangerous to play with fdtab before doing fd_insert()
because this last one is responsible for growing maxfd as needed.
Call fd_insert() before instead.
diff --git a/src/checks.c b/src/checks.c
index 0a27201..0996925 100644
--- a/src/checks.c
+++ b/src/checks.c
@@ -329,6 +329,7 @@
 						//fprintf(stderr, "process_chk: 4\n");
 			
 						s->curfd = fd; /* that's how we know a test is in progress ;-) */
+						fd_insert(fd);
 						fdtab[fd].owner = t;
 						fdtab[fd].cb[DIR_RD].f = &event_srv_chk_r;
 						fdtab[fd].cb[DIR_RD].b = NULL;
@@ -339,7 +340,6 @@
 #ifdef DEBUG_FULL
 						assert (!EV_FD_ISSET(fd, DIR_RD));
 #endif
-						fd_insert(fd);
 						/* FIXME: we allow up to <inter> for a connection to establish, but we should use another parameter */
 						tv_delayfrom(&t->expire, &now, s->inter);
 						task_queue(t);	/* restore t to its place in the task list */