rhbz#1286416: Be more resilient during auto-recovery attempts

...called from within the signal handler, so any bets are off

Change-Id: Iedb5c7bc8d08350e5f3e3118c6713f5c25b238b6
(cherry picked from commit 9b3ca276)
Reviewed-on: https://gerrit.libreoffice.org/20282Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Michael Stahl <mstahl@redhat.com>
(cherry picked from commit 85a4677c)

framework/source/services/autorecovery.cxx

@@ -2480,6 +2480,8 @@ void AutoRecovery::implts_registerDocument(const css::uno::Reference< css::frame
         return;
 
     css::uno::Reference< css::frame::XFrame >   xFrame   = xController->getFrame();
+    if (!xFrame.is())
+        return;
     css::uno::Reference< css::frame::XDesktop > xDesktop (xFrame->getCreator(), css::uno::UNO_QUERY);
     if (!xDesktop.is())
         return;