core dump when window is too short; infinite loop when too narrow

[Algorithm Petrofsky]

In GNU Emacs 21.1.1 (i586-pc-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2001-10-24 on radish.petrofsky.org

Please describe exactly what actions triggered the bug
and the precise symptoms of the bug:

-- Create a window with height two, but zero usable lines because
   mode-line-format and header-line-format are both non-nil:

     emacs -q
     C-u C-x 2 C-h i C-x o M-2 C-x ^ M-C-v

   Symptom: Fatal error (6).Aborted (core dumped)


-- Create a window with one usable column and try to display a two-column
   character:

     emacs -q --eval "(setq truncate-partial-width-windows nil)"
     M-10 C-x 3 C-x o M-7 C-x } C-x o C-h h M->

   Symptom: infinite loop.  (Must C-g C-g and dump core to stop.)


These happen with TERM=linux or TERM=screen.  Seems okay under X11.

Perhaps the minimum window height needs to be changed from two to
three, to ensure there is at least one body line.

-al