Don't add header to existing sources

[fgiust]

When the plugin is enabled, it always add the header
/** Eclipse Class Decompiler plugin, Copyright (c) 2017 Chen Chao. */
when opening an existing source file.
This is very very annoying, since it adds an additional line to original sources you are using for debug, so the debugger it's always off one line when debugging.
Could you please avoid that the header is added at least for existing sources? (removing it from any file would ever be better, I understand you want to highlight your work but this can be really annoying...)

[cnfree]

I merge one empty line or the first line after the comment line at the source code, so the debugger shouldn't off one line when debugging.

If it off one line, that's a bug.