Cleaner fix for Detaching notify write_cb issue
Cleaner fix for Detaching notify write_cb issue

NULL all debugger transport I/O callbacks (i.e. callbacks other than
detaching_cb) whenever the transport indicates an error has occurred.
By the API contract we're not allowed to call any of them after transport
read/write error so it's safest to NULL them all on a transport error.

This is not strictly necessary because only the write_cb is used by
detach1() currently before NULLing the callbacks anyway.  However, NULLing
them early on transport error ensures there's no potential to call them
incorrectly even when the code is reorganized later.

markand/duktape,harold-b/duktape,jmptrader/duktape,markand/duktape,jmptrader/duktape,svaarala/duktape,harold-b/duktape,harold-b/duktape,jmptrader/duktape,jmptrader/duktape,jmptrader/duktape,harold-b/duktape,svaarala/duktape,markand/duktape,markand/duktape,jmptrader/duktape,markand/duktape,svaarala/duktape,markand/duktape,harold-b/duktape,svaarala/duktape,svaarala/duktape,jmptrader/duktape,harold-b/duktape,svaarala/duktape,jmptrader/duktape,markand/duktape,jmptrader/duktape,markand/duktape,harold-b/duktape,markand/duktape,harold-b/duktape,svaarala/duktape,markand/duktape,jmptrader/duktape,svaarala/duktape,harold-b/duktape,svaarala/duktape,harold-b/duktape