fix(_comp_compgen_sysv_services): do not generate names in subdirs

This is a regression by Ref. [1].  In Ref. [1], I have replaced the
combination of "_comp_expand_glob" and "_comp_compgen -- -W" with
"_comp_compgen -C -- -f".  However, I realized that this strategy
would cause generation of the filenames in subdirectories when $cur
contains "/" [2].  To avoid this, one can exclude candidates
containing a slash by -X '*/*'.

[1] #1553
[2] #1639 (comment)

Author: akinomyoga

bash_completion

@@ -2215,7 +2215,7 @@ _comp_compgen_sysv_services()
     local sysvdirs
     _comp_sysvdirs &&
         _comp_compgen -U sysvdirs -C "${sysvdirs[0]}" -- \
-            -fX "@($_comp_backup_glob|functions|*.sh|README*)"
+            -fX "@($_comp_backup_glob|functions|*.sh|README*|*/*)"
 }
 
 # This function completes on services