Consistently refuse to create bitmaps with 0 width or height.

Homogenize the behaviour of all ports when creating bitmaps with 0 width or
height: just fail always as it doesn't seem to make sense to support this.

Closes #16828.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@78434 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/changes.txt

@@ -21,6 +21,9 @@ Changes in behaviour not resulting in compilation errors
   other ports, but this can be unexpected for the applications not expecting
   their idle handlers to be called from inside wxYield().
 
+- Creating wxBitmap with 0 width or height now always fails in all ports
+  (it used to succeed in wxMSW).
+
 Changes in behaviour which may result in build errors
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