Move SIGCHLD to client launch

SIG_DFL on SIGCHLD prevents proper functioning of pclose, which the new version of the pasting functionality requires.

Closes Cloudef#385

Ref: https://stackoverflow.com/questions/54189212/popen-returns-1-unexpectedly

client/bemenu-run.c

@@ -133,6 +133,14 @@ static inline void ignore_ret(int useless, ...) { (void)useless; }
 static void
 launch(const struct client *client, const char *bin)
 {
+    struct sigaction action = {
+        .sa_handler = SIG_DFL,
+        .sa_flags = SA_NOCLDWAIT
+    };
+
+    // do not care about childs
+    sigaction(SIGCHLD, &action, NULL);
+
     if (!bin)
         return;
 
@@ -166,14 +174,6 @@ item_cb(const struct client *client, struct bm_item *item)
 int
 main(int argc, char **argv)
 {
-    struct sigaction action = {
-        .sa_handler = SIG_DFL,
-        .sa_flags = SA_NOCLDWAIT
-    };
-
-    // do not care about childs
-    sigaction(SIGCHLD, &action, NULL);
-
     if (!bm_init())
         return EXIT_FAILURE;