winmm: Fix SEEK_END direction of mmio files without buffering.

dlls/winmm/mmio.c

@@ -127,7 +127,10 @@ static LRESULT CALLBACK mmioDosIOProc(LPMMIOINFO lpmmioinfo, UINT uMessage,
 	 * lParam2 = from whence to seek (SEEK_SET, SEEK_CUR, SEEK_END)
 	 * Returns: new file position, -1 on error
 	 */
-	ret = _llseek((HFILE)lpmmioinfo->adwInfo[0], (LONG)lParam1, (LONG)lParam2);
+	if (lParam2 == SEEK_END)
+	    ret = _llseek((HFILE)lpmmioinfo->adwInfo[0], -(LONG)lParam1, (LONG)lParam2);
+	else
+	    ret = _llseek((HFILE)lpmmioinfo->adwInfo[0], (LONG)lParam1, (LONG)lParam2);
 	if (ret != -1)
 	    lpmmioinfo->lDiskOffset = ret;
 	return ret;

dlls/winmm/tests/mmio.c

@@ -750,7 +750,7 @@ static void test_mmioSeek(void)
 
         /* seek backward from the end */
         pos = mmioSeek(hmmio, offset, SEEK_END);
-        todo_wine ok(pos == size-offset, "expected %d, got %d\n", size-offset, pos);
+        ok(pos == size-offset, "expected %d, got %d\n", size-offset, pos);
 
         mmioClose(hmmio, 0);
     }