lexical #3/3, collapse append(NULL) into cp_ccom()

the sequence
   orig_wlist = wlist;
   append(NULL);
   cp_ccom(wlist, ...);
 is transformed.

 expressions to care about in cp_ccom()
    C1 :=  (wlist->wl_next != NULL)
    C2 :=  (wlist->wl_word != NULL)
    C3 :=  wl_length(wlist)

    D1 :=  (orig_wlist != NULL)
    D2 :=  (orig_wlist->wl_word != NULL)
    D3 :=  wl_length(orig_wlist);

 cases and their significance in cp_ccom():
    orig_wlist = NULL;
    wlist = wl_cons(NULL, NULL);
      C1 == false
      D1 == false
      C2,C3 dont care

    orig_wlist = wl_cons(E1, wl_cons(E2, ... wl_cons(En, NULL)))
    wlist = wl_cons(E1, wl_cons(E2, .... wl_cons(En, wl_cons(NULL, NULL))))
     C1 == true
     D1 == true
     C2 === D2
     C3 === D3 + 1

src/frontend/parser/complete.c

@@ -94,11 +94,11 @@ cp_ccom(wordlist *wlist, char *buf, bool esc)
 
     buf = cp_unquote(copy(buf));
     cp_wstrip(buf);
-    if (wlist->wl_next) {   /* Not the first word. */
+    if (wlist) {   /* Not the first word. */
         cc = getccom(wlist->wl_word);
         if (cc && cc->cc_invalid)
             cc = NULL;
-        arg = wl_length(wlist) - 2;
+        arg = wl_length(wlist) - 1;
         if (arg > 3)
             arg = 3;
         /* First filenames. */

src/frontend/parser/lexical.c

@@ -256,7 +256,6 @@ gotchar:
                     goto done;
                 }
                 // cp_ccom doesn't mess wlist, read only access to wlist->wl_word
-                append(NULL);
                 cp_ccom(wlist, buf, FALSE);
                 wl_free(wlist);
                 (void) fputc('\r', cp_out);
@@ -291,7 +290,6 @@ gotchar:
 #else
 		    fputc(linebuf[j], cp_out);	/* But you can't edit */
 #endif
-                append(NULL);
                 // cp_ccom doesn't mess wlist, read only access to wlist->wl_word
                 cp_ccom(wlist, buf, TRUE);
                 wl_free(wlist);