Return the minimum size of WINDOW.
WINDOW must be a valid window and defaults to the selected one.
Optional argument HORIZONTAL non-nil means return the minimum
number of columns of WINDOW; otherwise return the minimum number
of WINDOW's lines.
Optional argument IGNORE, if non-nil, means ignore restrictions
imposed by fixed size windows, `window-min-height' or
`window-min-width' settings. If IGNORE equals `safe', live
windows may get as small as `window-safe-min-height' lines and
`window-safe-min-width' columns. If IGNORE is a window, ignore
restrictions for that window only. Any other non-nil value
means ignore all of the above restrictions for all windows.