raw-win32.c: Fix incorrect handling behaviour of small block files

It is a valid case that the read data's size is smaller than the
requested size since there could be files that are smaller than
the minimum block size (For ex. when a VMDK disk descriptor file)
Signed-off-by: NTal Kain <tal.kain@ravellosystems.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

block/raw-win32.c

@@ -85,6 +85,7 @@ static size_t handle_aiocb_rw(RawWin32AIOData *aiocb)
             ret_count = 0;
         }
         if (ret_count != len) {
+            offset += ret_count;
             break;
         }
         offset += len;