construct grouped ScFormulaCell with bDirty=true, fdo#79249 related

Noticed when loading
https://bugs.freedesktop.org/attachment.cgi?id=99844
with fdo#79249 fix where oox::xls::applyCellFormulas() groups the
consecutive =#N/A formulas. Only A1 result was displayed, other cells
were displayed empty.

Change-Id: I3a541f74d3d25e1515a1c6d47f02ec6a8e817c93

sc/source/core/data/formulacell.cxx

@@ -751,7 +751,7 @@ ScFormulaCell::ScFormulaCell(
     nSeenInIteration(0),
     cMatrixFlag ( cInd ),
     nFormatType(xGroup->mnFormatType),
-    bDirty(false),
+    bDirty(true),
     bChanged( false ),
     bRunning( false ),
     bCompile( false ),