LC_COLLATE: Fix last character ellipsis handling (Bug 22668)

During ellipsis processing the collation cursor was not correctly
moved to the end of the ellipsis after processing.

The code inserted the new entry after the cursor, but before the
real end of the ellipsis:
                                [cursor]
... element_t <-> element_t <-> element_t <-> element_t
                  "<U0000>"     "<U0001>"     "<U007F>"
                  startp                      endp

At the end of the function we have:

                  [cursor]
... element_t <-> element_t <-> element_t
                  "<U007E>"     "<U007F>"
                                endp

The cursor should be pointing at endp, the last element in the
doubly-linked list, otherwise when execution returns to the
caller we will start inserting the next line after <U007E>.

Subsequent operations end up unlinking the ellipsis end entry or
just leaving it in the list dangling from the end.  This kind of
dangling is immediately visible in C.UTF-8 with the following
sorting from strcoll:
<U0010FFFF>
<U0000FFFF>
<U000007FF>
<U0000007F>

With the cursor correctly adjusted the end entry is correctly given
the right location and thus the right weight.

Retested and no regressions on x86_64 and i686.

Co-authored-by: Carlos O'Donell <carlos@redhat.com>

locale/programs/ld-collate.c

@@ -1483,6 +1483,9 @@ order for `%.*s' already defined at %s:%Zu"),
 	    }
 	}
     }
+  /* Move the cursor to the last entry in the ellipsis.
+     Subsequent operations need to start from the last entry.  */
+  collate->cursor = endp;
 }