Display unformatted content if pretty printer fails

[sandraros]

Fix #25.

If the pretty-printer formatting fails, nothing is displayed. I didn't analyze the reason why the pretty printer is failing, anyway ABAP Cleaner is much more powerful and does the job fairly well.

While fixing it, I saw some code catching "cx_class_not_existent" errors to handle , but these exceptions are never raised. Instead I created a custom class "zcx_op_dve". I have kept the catching block of "cx_class_not_existent", remove it if you want. I have defined the variable "unformatted_content" because its name is displayed by "cl_demo_output".

[gepparta]

Hello @sandraros,

thank you for your contribution. Is it possible for you to provide a unit test for the non displaying errror?