Remove an assert in StgStreamImpl_Write()

[Mike McCormack]

Robert Shearman wrote:
> Francois Gouget wrote:
> 
>>
>> Changelog:
>>
>>  * dlls/ole32/stg_stream.c
>>
>>    Aric Stewart <aric at codeweavers.com>
>>    Remove an assert and instead just fail.
>>    This allows iTunes to finish installing with the reboot.
>>
> 
> A better fix would be to check the result of IStream_SetSize in this 
> function, although I think the original problem may well be fixed after 
> the STG_E_REVERTED checks.

If we can still run into the assert, a test case showing that would be 
welcome ...

Mike