Handle ambiguity in tui_partial_win_by_name
    
    This changes tui_partial_win_by_name to correctly handle an ambiguous
    name prefix.  This will be important once the user can register new
    window types.
    
    gdb/ChangeLog
    2020-02-22  Tom Tromey  <tom@tromey.com>
    
    	* tui/tui-win.c (tui_partial_win_by_name): Handle ambiguity
    	correctly.
    
    Change-Id: I59aaacd697eeab649164183457ef722dae58d60d