Make sure that at least one worksheet exist in the workbook

src/xlsx/xlsxworkbook.cpp

@@ -251,6 +251,8 @@ bool Workbook::renameWorksheet(int index, const QString &name)
 bool Workbook::deleteWorksheet(int index)
 {
     Q_D(Workbook);
+    if (d->worksheets.size() <= 1)
+        return false;
     if (index < 0 || index >= d->worksheets.size())
         return false;
     d->worksheets.removeAt(index);

tests/auto/document/tst_documenttest.cpp

@@ -343,8 +343,10 @@ void DocumentTest::testDeleteWorksheet()
     QCOMPARE(xlsx1.worksheetNames(), QStringList()<<"Sheet1"<<"Sheet3");
     xlsx1.deleteWorksheet("Sheet1");
     QCOMPARE(xlsx1.worksheetNames(), QStringList()<<"Sheet3");
-//    xlsx1.deleteWorksheet("Sheet3");
-//    QCOMPARE(xlsx1.worksheetNames(), QStringList()<<"Sheet4");
+
+    //Cann't delete the last worksheet
+    xlsx1.deleteWorksheet("Sheet3");
+    QCOMPARE(xlsx1.worksheetNames(), QStringList()<<"Sheet3");
 }
 
 QTEST_APPLESS_MAIN(DocumentTest)