tdf#120657 Pie chart saved as DOC doesn't preview in MSO

regression from

    commit 9ec8bf8f
    add SvStream::TellEnd

the problem is that in this stack trace

    sot/source/sdstor/stgelem.hxx:130
    sot/source/sdstor/stgdir.cxx:300
    sot/source/sdstor/stg.cxx:245
    sot/source/sdstor/storage.cxx:187
    tools/source/stream/stream.cxx:1908
    sw/source/filter/ww8/ww8scan.cxx:6267

The StgEntry returns a size of 0. If we do something else to the
SotStorageStream first, then it materialises a temporary stream, and
that stream returns a valid size.

Also implement suggestions from mike kaganski:

IMO, it would be more robust to implement this new function as virtual
(instead of the remainingSize()), and reimplement the latter as
non-virtual one using the new one and doing the necessary correction.

Change-Id: Id1462d918570a684ec67099c30181436a27d3c6a
Reviewed-on: https://gerrit.libreoffice.org/62984
Tested-by: Jenkins
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

include/sot/storage.hxx

@@ -56,7 +56,7 @@ public:
     void                CopyTo( SotStorageStream * pDestStm );
     bool                Commit();
     bool                SetProperty( const OUString& rName, const css::uno::Any& rValue );
-    virtual sal_uInt64 remainingSize() override;
+    virtual sal_uInt64  TellEnd() override;
 };
 
 class  BaseStorage;

include/tools/stream.hxx

@@ -272,9 +272,9 @@ public:
     sal_uInt64      Seek( sal_uInt64 nPos );
     sal_uInt64      SeekRel( sal_Int64 nPos );
     sal_uInt64      Tell() const { return m_nBufFilePos + m_nBufActualPos;  }
-    sal_uInt64      TellEnd();
+    virtual sal_uInt64 TellEnd();
     // length between current (Tell()) pos and end of stream
-    virtual sal_uInt64 remainingSize();
+    sal_uInt64      remainingSize();
     void            Flush();
     // next Tell() <= nSize
     bool            SetStreamSize( sal_uInt64 nSize );
@@ -669,7 +669,7 @@ public:
 
     void            ObjectOwnsMemory( bool bOwn ) { bOwnsData = bOwn; }
     void            SetResizeOffset( std::size_t nNewResize ) { nResize = nNewResize; }
-    virtual sal_uInt64 remainingSize() override { FlushBuffer(true); return GetEndOfData() - Tell(); }
+    virtual sal_uInt64 TellEnd() override { FlushBuffer(true); return nEndOfData; }
 };
 
 #endif

sot/source/sdstor/storage.cxx

@@ -181,12 +181,16 @@ sal_uInt32 SotStorageStream::GetSize() const
     return nSize;
 }
 
-sal_uInt64 SotStorageStream::remainingSize()
+sal_uInt64 SotStorageStream::TellEnd()
 {
+    // Need to flush the buffer so we materialise the stream and return the correct answer
+    // otherwise we return a 0 value from StgEntry::GetSize
+    FlushBuffer(true);
+
     if (pOwnStm)
-        return pOwnStm->GetSize() - Tell();
+        return pOwnStm->GetSize();
 
-    return SvStream::remainingSize();
+    return SvStream::TellEnd();
 }
 
 void SotStorageStream::CopyTo( SotStorageStream * pDestStm )

tools/source/stream/stream.cxx

@@ -1425,12 +1425,21 @@ bool checkSeek(SvStream &rSt, sal_uInt64 nOffset)
 sal_uInt64 SvStream::remainingSize()
 {
     sal_uInt64 const nCurr = Tell();
-    sal_uInt64 const nEnd = Seek(STREAM_SEEK_TO_END);
+    sal_uInt64 const nEnd = TellEnd();
     sal_uInt64 nMaxAvailable = nEnd > nCurr ? (nEnd-nCurr) : 0;
     Seek(nCurr);
     return nMaxAvailable;
 }
 
+sal_uInt64 SvStream::TellEnd()
+{
+    FlushBuffer(true);
+    sal_uInt64 const nCurr = Tell();
+    sal_uInt64 const nEnd = Seek(STREAM_SEEK_TO_END);
+    Seek(nCurr);
+    return nEnd;
+}
+
 void SvStream::Flush()
 {
     FlushBuffer(m_isConsistent);
@@ -1903,11 +1912,6 @@ void SvMemoryStream::SetSize(sal_uInt64 const nNewSize)
     ReAllocateMemory( nDiff );
 }
 
-sal_uInt64 SvStream::TellEnd()
-{
-    return Tell() + remainingSize();
-}
-
 //Create a OString of nLen bytes from rStream
 OString read_uInt8s_ToOString(SvStream& rStrm, std::size_t nLen)
 {