Plot Overwrite - Warning instead of Error

[niederle]

1. check "Don't Overwrite" option in the plot-node configuration
2. Execute -> fine, file is written
   Now:
3. Execute -> error, file exists, no plot view created

This is fine, but there should be an option to disable the output file without removing the file path.
The idea is to create another checkbox to enable or disable writing the plot to file.