I would suggest to prevent the ESC key from interrupting the F12 rendering.
Such feature is hard coded and cannot be disabled by the user in any way.
The reason for this change is that the escape key is used so often in Blender, by me at least, that if you keep on working during the render, it is almost impossible to avoid to press it sooner or later (unintentionally of course), and then to lose the whole rendering in progress.
On the other hand there are other quick ways to deliberately stop the rendering, and you have not to do it so often I suppose.
Another option would be to restrict this function of the ESC key for just when the render window is visible in the interface.
What do you think about?