unipoll: get SolarMutex lock counting right.

lo_startmain drops the SolarMutex without taking it, interestingly.

Change-Id: I2280e2fa6acb8739f970983032db72a8241d1c4f
Reviewed-on: https://gerrit.libreoffice.org/71742Reviewed-by: Jan Holesovsky <kendy@collabora.com>
Tested-by: Jan Holesovsky <kendy@collabora.com>

desktop/source/lib/init.cxx

@@ -4626,6 +4626,7 @@ static void lo_runLoop(LibreOfficeKit* /*pThis*/,
     SolarMutexGuard aGuard;
     vcl::lok::registerPollCallbacks(pPollCallback, pWakeCallback, pData);
     lo_startmain(nullptr);
+    Application::AcquireSolarMutex(1); // startmain releases it.
 }
 
 static bool bInitialized = false;