Move declarations to beginning of switch statements

Move declarations to beginning of switch statements

Several variable declarations were recently added immediately after
labels, but this causes compile errors in GCC versions prior to 11,
e.g.,

    wsmap.c: In function ‘handle_event’:
    wsmap.c:534:4: error: a label can only be part of a statement and a declaration is not a statement
      534 |    WMScreen *wmscr = wsmap->scr->wmscreen;
          |    ^~~~~~~~

We move these declarations to the top of the corresponding switch
statements so that Window Maker can compile on these older versions of
GCC.