Add support for cells in error when writing XLSX and ODS

When appending data to an existing sheet, it was possible to get cells in error when reading (DIV/0 for instance). When trying to write them back, `addRow` would throw because `Cell`s in error were not supported by the writers.

src/Spout/Writer/XLSX/Manager/WorksheetManager.php

@@ -218,6 +218,9 @@ EOD;
             $cellXML .= ' t="b"><v>' . (int) ($cell->getValue()) . '</v></c>';
         } elseif ($cell->isNumeric()) {
             $cellXML .= '><v>' . $cell->getValue() . '</v></c>';
+        } elseif ($cell->isError() && is_string($cell->getValueEvenIfError())) {
+            // only writes the error value if it's a string
+            $cellXML .= ' t="e"><v>' . $cell->getValueEvenIfError() . '</v></c>';
         } elseif ($cell->isEmpty()) {
             if ($this->styleManager->shouldApplyStyleOnEmptyCell($styleId)) {
                 $cellXML .= '/>';