gdiplus: Fix pointer math for the 64-bit tests.

dlls/gdiplus/gdiplus.c

@@ -407,7 +407,7 @@ BOOL lengthen_path(GpPath *path, INT len)
 void convert_32bppARGB_to_32bppPARGB(UINT width, UINT height,
     BYTE *dst_bits, INT dst_stride, const BYTE *src_bits, INT src_stride)
 {
-    UINT x, y;
+    INT x, y;
     for (y=0; y<height; y++)
     {
         const BYTE *src=src_bits+y*src_stride;

dlls/gdiplus/image.c

@@ -1404,7 +1404,7 @@ GpStatus WINGDIPAPI GdipCreateHBITMAPFromBitmap(GpBitmap* bitmap,
     if (result)
     {
         lockeddata.Stride = -width * 4;
-        lockeddata.Scan0 = bits - (lockeddata.Stride * (height - 1));
+        lockeddata.Scan0 = bits + (width * 4 * (height - 1));
 
         stat = GdipBitmapLockBits(bitmap, NULL, ImageLockModeRead|ImageLockModeUserInputBuf,
             PixelFormat32bppPARGB, &lockeddata);