windowscodecs: Mark some fall-throughs in switch statements.

dlls/windowscodecs/pngformat.c

@@ -364,6 +364,7 @@ static HRESULT WINAPI PngDecoder_Initialize(IWICBitmapDecoder *iface, IStream *p
     case PNG_COLOR_TYPE_GRAY_ALPHA:
         /* WIC does not support grayscale alpha formats so use RGBA */
         ppng_set_gray_to_rgb(This->png_ptr);
+        /* fall through */
     case PNG_COLOR_TYPE_RGB_ALPHA:
         This->bpp = bit_depth * 4;
         switch (bit_depth)

dlls/windowscodecs/tiffformat.c

@@ -295,6 +295,7 @@ static HRESULT tiff_get_decode_info(TIFF *tiff, tiff_decode_info *decode_info)
     {
     case 0: /* WhiteIsZero */
         decode_info->invert_grayscale = 1;
+        /* fall through */
     case 1: /* BlackIsZero */
         if (samples != 1)
         {