Provide operator-- on SortedCellIndexIterator to fix #220

src/db/db/dbCellMapping.cc

@@ -81,6 +81,18 @@ struct SortedCellIndexIterator
     return *this;
   }
 
+  SortedCellIndexIterator &operator--()
+  {
+    --m_n;
+    return *this;
+  }
+
+  SortedCellIndexIterator &operator-=(size_t n)
+  {
+    m_n -= n;
+    return *this;
+  }
+
   bool operator==(const SortedCellIndexIterator &d) const
   {
     return m_n == d.m_n;