WIN revert to Sleep(1) for yield

There are multiple ways on Windows to yield a thread:

* SwitchToThread: yields to any thread on same processor
* Sleep(0): yields to any thread of same or higher priority
            on any processor
* Sleep(1): yields to any thread on any processor

So we stay with Sleep(1), as it also seems the only call, which
actually does some sleep and is not a busy wait.

Change-Id: I85c69b2f32dba9869bbddc1a572b3a63c366c5d1

vcl/win/app/salinst.cxx

@@ -618,7 +618,7 @@ bool WinSalInstance::DoYield(bool bWait, bool bHandleAllCurrentEvents, sal_uLong
 
         // #i18883# only sleep if potential deadlock scenario, ie, when a dialog is open
         if( ImplGetSVData()->maAppData.mnModalMode )
-            SwitchToThread();
+            Sleep(1);
         else
             bDidWork = SendMessageW( mhComWnd, SAL_MSG_THREADYIELD, (WPARAM)bWait, (LPARAM)bHandleAllCurrentEvents );