riched32: Fix the extra window bytes count for 64-bit.

dlls/riched32/richedit.c

@@ -59,7 +59,7 @@ static BOOL RICHED32_Register(void)
     wndClass.style = CS_DBLCLKS | CS_HREDRAW | CS_VREDRAW | CS_GLOBALCLASS;
     wndClass.lpfnWndProc = RichEdit10ANSIWndProc;
     wndClass.cbClsExtra = 0;
-    wndClass.cbWndExtra = 4;
+    wndClass.cbWndExtra = sizeof(void *);
     wndClass.hCursor = LoadCursorA(0, (LPSTR)IDC_ARROW);
     wndClass.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1);
     wndClass.lpszClassName = RICHEDIT_CLASS10A; /* WC_RICHED32A; */