shell: remember unmaximized window size

Evince tries to save the window size and maximization state for each document and restores them when the document is reopened. However, for maximized documents, Evince does not correctly save and restore the window size. If a document is opened in a maximized state and later unmaximized, the window is restored to the default 600x600 size instead of the window's size prior to maximization.

This fixes how Evince saves and restores the window size for maximized documents.