cabinet: Mark some fall-throughs in switch statements.

dlls/cabinet/fci.c

@@ -466,10 +466,13 @@ static cab_ULONG fci_get_checksum( const void *pv, UINT cb, cab_ULONG seed )
   switch (cb % 4) {
     case 3:
       ul |= (((ULONG)(*pb++)) << 16);
+      /* fall through */
     case 2:
       ul |= (((ULONG)(*pb++)) <<  8);
+      /* fall through */
     case 1:
       ul |= *pb;
+      /* fall through */
     default:
       break;
   }

dlls/cabinet/fdi.c

@@ -360,7 +360,9 @@ static cab_ULONG checksum(const cab_UBYTE *data, cab_UWORD bytes, cab_ULONG csum
 
   switch (bytes & 3) {
   case 3: ul |= *data++ << 16;
+  /* fall through */
   case 2: ul |= *data++ <<  8;
+  /* fall through */
   case 1: ul |= *data;
   }
   csum ^= ul;