Ignore null commands in command list

Commands typically become null in the command list when there’s been a
change to a command script (e.g. upgrading to a new version of Fungus).
It’s better to just ignore this rather than cause a null exception.

Assets/Fungus/Flowchart/Scripts/Commands/If.cs

@@ -106,6 +106,11 @@ namespace Fungus
 			{
 				Command nextCommand = parentBlock.commandList[i];
 
+				if (nextCommand == null)
+				{
+					continue;
+				}
+
 				// Find next command at same indent level as this If command
 				// Skip disabled commands, comments & labels
 				if (!nextCommand.enabled ||