tdf#129412: Crash when registered data source is not available

See bt here:
https://bugs.documentfoundation.org/show_bug.cgi?id=129412#c4

Regression from:
https://cgit.freedesktop.org/libreoffice/core/commit/?id=9009663deb8f0862f419fd99bf0b761c7f923eff

author	Tomaž Vajngerl <tomaz.vajngerl@collabora.co.uk>	2017-02-26 22:48:06 +0100
committer	Tomaž Vajngerl <quikee@gmail.com>	2017-04-04 13:39:29 +0000
commit	9009663deb8f0862f419fd99bf0b761c7f923eff (patch)
tree	ea25976de0919f9d2161037d83be0eace4c1070b
parent	1931b5b01c6fdaa204d26ec4b9675dad16373cf2 (diff)
tdf#83257 [API-CHANGE] Pivot chart implementation

Change-Id: Ib4de665f6e5380baf51589c92473ad88e8c9b84e
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/87096
Tested-by: Jenkins
Reviewed-by: Tomaž Vajngerl <quikee@gmail.com>
Signed-off-by: xisco <xiscofauli@libreoffice.org>
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/87125
diff --git a/sc/source/ui/unoobj/PivotTableDataProvider.cxx b/sc/source/ui/unoobj/PivotTableDataProvider.cxx
index 52c657e..1d10623 100644
--- a/sc/source/ui/unoobj/PivotTableDataProvider.cxx
+++ b/sc/source/ui/unoobj/PivotTableDataProvider.cxx
@@ -284,6 +284,8 @@
    m_aFieldOutputDescriptionMap.clear();

    uno::Reference<sheet::XDataPilotResults> xDPResults(pDPObject->GetSource(), uno::UNO_QUERY);
    if (!xDPResults.is())
        return;
    uno::Sequence<uno::Sequence<sheet::DataResult>> xDataResultsSequence = xDPResults->getResults();

    double fNan;