When a user has opened a temporary window and resized it, if they then
request that window to be opened again (like what might happen when
re-rendering with F12 etc.) blender would resize the already open
window unnecessarily; often to the dismay of the user who has adjusted
it prior.

This would most typically affect Preferences and Render Result windows
by default. This patch will prevent blender from resizing if they are
already open.