tdf#127192 Printing in main thread

the wollmux has change the dialogs form swing to the LO-Dialogs,
and when printig with MS-PDF then LO hang on this line.
The reason is wollmux run in it own thread, but this thread has
no win-message-pump, when the printer-driver would open the
FileSave-Dialog then it hangs, because the message-pump
is missing in this thread.

The swing has made it own win-message-pump for this
thread.

Change-Id: Ia5131464dcc5f166133a3302d29550e945dd1026
Reviewed-on: https://gerrit.libreoffice.org/78170
Reviewed-by: Jan-Marek Glogowski <glogow@fbihome.de>
Reviewed-by: Juergen Funk (CIB) <juergen.funk_ml@cib.de>
Tested-by: Juergen Funk (CIB) <juergen.funk_ml@cib.de>

vcl/win/gdi/salprn.cxx

@@ -52,6 +52,8 @@
 #include <com/sun/star/lang/XInitialization.hpp>
 #include <comphelper/processfactory.hxx>
 
+#include <vcl/threadex.hxx>
+
 #include <malloc.h>
 
 #include <winspool.h>
@@ -1502,8 +1504,8 @@ bool WinSalPrinter::StartJob( const OUString* pFileName,
     else
         aInfo.lpszOutput = nullptr;
 
-    // start Job
-    int nRet = lcl_StartDocW( hDC, &aInfo, this );
+    // start Job, in the main thread
+    int nRet = vcl::solarthread::syncExecute([hDC, this, &aInfo]() -> int { return lcl_StartDocW(hDC, &aInfo, this); });
 
     if ( nRet <= 0 )
     {