[lmi] MDI resize assertion failure

[Greg Chicares]

Symptom:

  Error
  Assertion '"w > 0 && h > 0"' failed
  (invalid bitmap size).
  [file ../src/msw/bitmap.cpp, line 758]

To reproduce (at least with msw-xp):

  File | New | Illustration | OK
  alt-hyphen-X [or click the MDI child's maximize box]
  resize the application to the "wrong" size

Let me try to explain what the "wrong" size is. First, width doesn't seem to
matter at all. The "wrong" height is approximately one for which the toolbar
buttons are all shown, but the "white" window just vanishes. (I say "white"
because I can never remember if it's the application's client window, the
mdi parent frame or something else; but it is distinctively white, at least
with the "classic" msw-xp theme.)

Once you reach the exact height that triggers the assertion, it's retriggered
every time you cycle between alt-Spacebar-X and alt-Spacebar-R, which I guess
others conceptualize as maximizing and restoring the application.

No message appears on the console.

I speculate that it's an MDI thing, because if you do alt-hyphen-R, then
maximizing and restoring the application fails to retrigger the assertion.
Speculating wildly, might the assertion refer to the MDI child scrollbars,
or their up and down arrows?

Although I don't think it matters, I'll mention that I've turned off all the
gee-whiz graphics effects like animated menus.