make sure ScConditionEntry::Interpret() doesn't confuse calc threading

ScConditionEntry::Interpret() creates a temporary cell and interprets it
without it actually being in the document at the specified position,
which threading relies upon.

Change-Id: I06fcc11dfbe14e715de4c173e061064ac90da990
Reviewed-on: https://gerrit.libreoffice.org/63182
Tested-by: Jenkins
Reviewed-by: Luboš Luňák <l.lunak@collabora.com>

sc/source/core/data/column2.cxx

@@ -2902,8 +2902,11 @@ void ScColumn::SetFormulaResults( SCROW nRow, const double* pResults, size_t nLe
     sc::CellStoreType::position_type aPos = maCells.position(nRow);
     sc::CellStoreType::iterator it = aPos.first;
     if (it->type != sc::element_type_formula)
+    {
         // This is not a formula block.
+        assert( false );
         return;
+    }
 
     size_t nBlockLen = it->size - aPos.second;
     if (nBlockLen < nLen)
@@ -2934,8 +2937,11 @@ void ScColumn::CalculateInThread( ScInterpreterContext& rContext, SCROW nRow, si
     sc::CellStoreType::position_type aPos = maCells.position(nRow);
     sc::CellStoreType::iterator it = aPos.first;
     if (it->type != sc::element_type_formula)
+    {
         // This is not a formula block.
+        assert( false );
         return;
+    }
 
     size_t nBlockLen = it->size - aPos.second;
     if (nBlockLen < nLen)
@@ -2962,8 +2968,11 @@ void ScColumn::HandleStuffAfterParallelCalculation( SCROW nRow, size_t nLen )
     sc::CellStoreType::position_type aPos = maCells.position(nRow);
     sc::CellStoreType::iterator it = aPos.first;
     if (it->type != sc::element_type_formula)
+    {
         // This is not a formula block.
+        assert( false );
         return;
+    }
 
     size_t nBlockLen = it->size - aPos.second;
     if (nBlockLen < nLen)

sc/source/core/data/formulacell.cxx

@@ -4523,6 +4523,21 @@ bool ScFormulaCell::InterpretFormulaGroup()
         return false;
     }
 
+    if( forceType != ForceCalculationNone )
+    {
+        // ScConditionEntry::Interpret() creates a temporary cell and interprets it
+        // without it actually being in the document at the specified position.
+        // That would confuse opencl/threading code, as they refer to the cell group
+        // also using the position. This is normally not triggered (single cells
+        // are normally not in a cell group), but if forced, check for this explicitly.
+        if( pDocument->GetFormulaCell( aPos ) != this )
+        {
+            mxGroup->meCalcState = sc::GroupCalcDisabled;
+            aScope.addMessage("cell not in document");
+            return false;
+        }
+    }
+
     // Guard against endless recursion of Interpret() calls, for this to work
     // ScFormulaCell::InterpretFormulaGroup() must never be called through
     // anything else than ScFormulaCell::Interpret(), same as