Merge pull request #476 from AntonyCorbett/small_dictionary_perf

prevent double lookup

Source/QuestPDF/Elements/Table/Table.cs

@@ -80,7 +80,7 @@ namespace QuestPDF.Elements.Table
 
             CellsCache = Enumerable
                 .Range(0, MaxRow + 1)
-                .Select(x => groups.ContainsKey(x) ? groups[x] : Array.Empty<TableCell>())
+                .Select(x => groups.TryGetValue(x, out var value) ? value : Array.Empty<TableCell>())
                 .ToArray();
         }