tdf#136133: AppendInfoBar can return null

2 cases:
1) When set Donate property to false value in /org.openoffice.Office.UI.Infobar/Enabled
 and LastTimeDonateShow with 1 in /org.openoffice.Setup/Product (Expert Configuration)
See https://bugs.documentfoundation.org/attachment.cgi?id=164702

2) GetInvolved = false and LastTimeGetInvolved = 1
See https://bugs.documentfoundation.org/attachment.cgi?id=164703

Change-Id: I2da22616fb6f3fb4e42bf6b5e5c29cc094dc2fd6
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/101391
Tested-by: Jenkins
Reviewed-by: Julien Nabet <serval2412@yahoo.fr>
diff --git a/sfx2/source/view/viewfrm.cxx b/sfx2/source/view/viewfrm.cxx
index b0f1e40..9e4b4b2 100644
--- a/sfx2/source/view/viewfrm.cxx
+++ b/sfx2/source/view/viewfrm.cxx
@@ -1382,11 +1382,14 @@ void SfxViewFrame::Notify( SfxBroadcaster& /*rBC*/, const SfxHint& rHint )

                    VclPtr<SfxInfoBarWindow> pInfoBar = AppendInfoBar("getinvolved", "", SfxResId(STR_GET_INVOLVED_TEXT), InfobarType::INFO);

                    VclPtrInstance<PushButton> xGetInvolvedButton(&GetWindow());
                    xGetInvolvedButton->SetText(SfxResId(STR_GET_INVOLVED_BUTTON));
                    xGetInvolvedButton->SetSizePixel(xGetInvolvedButton->GetOptimalSize());
                    xGetInvolvedButton->SetClickHdl(LINK(this, SfxViewFrame, GetInvolvedHandler));
                    pInfoBar->addButton(xGetInvolvedButton);
                    if (pInfoBar)
                    {
                        VclPtrInstance<PushButton> xGetInvolvedButton(&GetWindow());
                        xGetInvolvedButton->SetText(SfxResId(STR_GET_INVOLVED_BUTTON));
                        xGetInvolvedButton->SetSizePixel(xGetInvolvedButton->GetOptimalSize());
                        xGetInvolvedButton->SetClickHdl(LINK(this, SfxViewFrame, GetInvolvedHandler));
                        pInfoBar->addButton(xGetInvolvedButton);
                    }
                }

                if (bUpdateLastTimeGetInvolvedShown
@@ -1408,12 +1411,14 @@ void SfxViewFrame::Notify( SfxBroadcaster& /*rBC*/, const SfxHint& rHint )
                    bUpdateLastTimeDonateShown = true;

                    VclPtr<SfxInfoBarWindow> pInfoBar = AppendInfoBar("donate", "", SfxResId(STR_DONATE_TEXT), InfobarType::INFO);

                    VclPtrInstance<PushButton> xDonateButton(&GetWindow());
                    xDonateButton->SetText(SfxResId(STR_DONATE_BUTTON));
                    xDonateButton->SetSizePixel(xDonateButton->GetOptimalSize());
                    xDonateButton->SetClickHdl(LINK(this, SfxViewFrame, DonationHandler));
                    pInfoBar->addButton(xDonateButton);
                    if (pInfoBar)
                    {
                        VclPtrInstance<PushButton> xDonateButton(&GetWindow());
                        xDonateButton->SetText(SfxResId(STR_DONATE_BUTTON));
                        xDonateButton->SetSizePixel(xDonateButton->GetOptimalSize());
                        xDonateButton->SetClickHdl(LINK(this, SfxViewFrame, DonationHandler));
                        pInfoBar->addButton(xDonateButton);
                    }
                }

                if (bUpdateLastTimeDonateShown