explorerframe/tests: Use SetRect() instead of open coding it.

[Michael Stefaniuc]

On 07/09/2016 02:09 PM, Marvin wrote:
> While running your changed tests on Windows, I think I found new failures.
> Being a bot and all I'm not very good at pattern recognition, so I might be
> wrong, but could you please double-check?
> Full results can be found at
> https://testbot.winehq.org/JobDetails.pl?Key=24129
> 
> Your paranoid android.
> 
> 
> === w7pro64 (64 bit nstc) ===
> nstc.c:1953: Test failed: Got event 17, count 1
This is a spurious error on Win7 according to the daily test results.
For whatever reason it seems to fail more reliable when run standalone
as all my 3 patches produced it.

bye
      michael