Under Application::IsOnSystemEventLoop, do nothing in Application::Reschedule

...as e.g. loading an HTML document via SwHTMLParser calls it at various places,
presumably to make loading more responsive for the user, but without any
functional impact beyond that.  So instead of aborting better just do nothing.

Change-Id: I99350ab98b1b75be9a8c7adcc72973174bc258e0
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/171688
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <stephan.bergmann@allotropia.de>

vcl/source/app/svapp.cxx

@@ -399,7 +399,7 @@ bool Application::Reschedule( bool i_bAllEvents )
     if (bAbort)
     {
         SAL_WARN("vcl.schedule", "Application::Reschedule(" << i_bAllEvents << ")");
-        std::abort();
+        return false;
     }
     return ImplYield(false, i_bAllEvents);
 }