fixed noselect bug when line is selected and one clicks on a blank canvas...

fixed noselect bug when line is selected and one clicks on a blank canvas which should also deselect selected line. also made pd_extrapath struct global as part of s_stuff.h so that ggee/image can use dynamic descriptors for retrieving of files (.e.g @pd_extra is translated to the pd's system-wide location of the extra/ folder)