[MonoDevelop] Right mouse click on bookmarks/breakpoints panel after last line.

[Ventsislav Mladenov]

Hi, 
   I found bug - if I click with right mouse button on left panel where 
bookmarks and breakpoints are placed I get ArgumentException "Line < MinLine"
This is because OnIconButtonPress in method of SourceEditorView  
args.LineNumber == 0 and it is passed to TextEditor.Caret.Line. 

I'm thinking that this is a bug and have to be fixed. 
There are two possible fixes:
1. Add one check in OnIconButtonPress 
if (args.LineNumber < Mono.TextEditor.DocumentLocation.MinLine)
   return;
2. args.LineNumber should point to the latest line of file.