At least during JunitTest_sw_unoapi_4
sw.SwXTextTable::com::sun::star::text::TextTable::TableColumnSeparators, some
SwFormatFrameSize is created with a width of USHRT_MAX ("Set USHRT_MAX as the
Table's default SSize") in SwDoc::InsertTable
(sw/source/core/docnode/ndtbl.cxx).  In SwTabFrame::Format
(sw/source/core/layout/tabfrm.cxx) that leads to nWishedTableWidth with a value
near USHRT_MAX and substantially larger than nMax, causing nLeftSpacing to be a
large negative value in the text::HoriOrientation::CENTER case.  That in turn
causes SwTextAdjuster::CalcRightMargin (sw/source/core/text/itradj.cxx) to
set

    pRight->PrtWidth( sal_uInt16( nRealWidth - nPrtWidth ) );

with a value of 32768 (where pRight is a SwGluePortion).  And a later call to
that SwGluePortion's GetPrtGlue would try to convert that 32768 to 'short',
getting flagged by Clang's -fsanitize=implicit-signed-integer-truncation.

In addition to changing GetPrtGlue (and MoveGlue) to use 'long' instead of
'short', drop some unncessary narrowing casts from client code.

Change-Id: I6a0d763acfad1fc3b550ec6107adf9f5429dd005
Reviewed-on: https://gerrit.libreoffice.org/68253
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>