fix incorrect exception raised while processing a list that exceeds MAX_ITEMS_TO_HANDLE

[baek9]

Environment data

• PTVSD version: 4.2.6
• OS and version: Windows 10
• Python version (& distribution if applicable, e.g. Anaconda): 2.7.6
• Using VS Code or Visual Studio: VS Code

Actual behavior

in VS Code, I ran following code and set a breakpoint to the print line and expand the lst in the debugging window. the code is:

lst = {}
for idx in range(0, 400):
    lst[idx] = ("blah")

print "break here and expand the lst in the debugging window"

And give this traceback:

Traceback (most recent call last):
  File "c:\Users\test\.vscode\extensions\ms-python.python-2019.3.6352\pythonFiles\lib\python\ptvsd\_vendored\pydevd\_pydevd_bundle\pydevd_frame.py", line 590, in
trace_dispatch
    self.do_wait_suspend(thread, frame, event, arg)
  File "c:\Users\test\.vscode\extensions\ms-python.python-2019.3.6352\pythonFiles\lib\python\ptvsd\_vendored\pydevd\_pydevd_bundle\pydevd_frame.py", line 78, in do_wait_suspend
    self._args[0].do_wait_suspend(*args, **kwargs)
  File "c:\Users\test\.vscode\extensions\ms-python.python-2019.3.6352\pythonFiles\lib\python\ptvsd\_vendored\pydevd\pydevd.py", line 1285, in do_wait_suspend
    keep_suspended = self._do_wait_suspend(thread, frame, event, arg, suspend_type, from_this_thread, frames_tracker)
  File "c:\Users\test\.vscode\extensions\ms-python.python-2019.3.6352\pythonFiles\lib\python\ptvsd\_vendored\pydevd\pydevd.py", line 1307, in _do_wait_suspend
    self.process_internal_commands()
  File "c:\Users\test\.vscode\extensions\ms-python.python-2019.3.6352\pythonFiles\lib\python\ptvsd\_vendored\pydevd\pydevd.py", line 1024, in process_internal_commands
    int_cmd.do_it(self)
  File "c:\Users\test\.vscode\extensions\ms-python.python-2019.3.6352\pythonFiles\lib\python\ptvsd\_vendored\pydevd\_pydevd_bundle\pydevd_comm.py", line 485, in do_it
    self.method(dbg, *self.args, **self.kwargs)
  File "c:\Users\test\.vscode\extensions\ms-python.python-2019.3.6352\pythonFiles\lib\python\ptvsd\_vendored\pydevd\_pydevd_bundle\pydevd_comm.py", line 655, in internal_get_variable_json
    for child_var in variable.get_children_variables(fmt=fmt):
  File "c:\Users\test\.vscode\extensions\ms-python.python-2019.3.6352\pythonFiles\lib\python\ptvsd\_vendored\pydevd\_pydevd_bundle\pydevd_suspended_frames.py", line 108, in get_children_variables
    for key, val, evaluate_name in lst:
ValueError: need more than 2 values to unpack
Traceback (most recent call last):
  File "c:\Users\test\.vscode\extensions\ms-python.python-2019.3.6352\pythonFiles\ptvsd_launcher.py", line 45, in <module>
    main(ptvsdArgs)
  File "c:\Users\test\.vscode\extensions\ms-python.python-2019.3.6352\pythonFiles\lib\python\ptvsd\__main__.py", line 391, in main
    run()
  File "c:\Users\test\.vscode\extensions\ms-python.python-2019.3.6352\pythonFiles\lib\python\ptvsd\__main__.py", line 272, in run_file
    runpy.run_path(target, run_name='__main__')
  File "C:\Python27\lib\runpy.py", line 252, in run_path
    return _run_module_code(code, init_globals, run_name, path_name)
  File "C:\Python27\lib\runpy.py", line 82, in _run_module_code
    mod_name, mod_fname, mod_loader, pkg_name)
  File "C:\Python27\lib\runpy.py", line 72, in _run_code
    exec code in run_globals
  File "d:\test.py", line 5, in <module>
    print "break here and expand the lst in debugging window"
  File "d:\test.py", line 5, in <module>
    print "break here and expand the lst in debugging window"
  File "c:\Users\test\.vscode\extensions\ms-python.python-2019.3.6352\pythonFiles\lib\python\ptvsd\_vendored\pydevd\_pydevd_bundle\pydevd_frame.py", line 590, in
trace_dispatch
    self.do_wait_suspend(thread, frame, event, arg)
  File "c:\Users\test\.vscode\extensions\ms-python.python-2019.3.6352\pythonFiles\lib\python\ptvsd\_vendored\pydevd\_pydevd_bundle\pydevd_frame.py", line 78, in do_wait_suspend
    self._args[0].do_wait_suspend(*args, **kwargs)
  File "c:\Users\test\.vscode\extensions\ms-python.python-2019.3.6352\pythonFiles\lib\python\ptvsd\_vendored\pydevd\pydevd.py", line 1285, in do_wait_suspend
    keep_suspended = self._do_wait_suspend(thread, frame, event, arg, suspend_type, from_this_thread, frames_tracker)
  File "c:\Users\test\.vscode\extensions\ms-python.python-2019.3.6352\pythonFiles\lib\python\ptvsd\_vendored\pydevd\pydevd.py", line 1307, in _do_wait_suspend
    self.process_internal_commands()
  File "c:\Users\test\.vscode\extensions\ms-python.python-2019.3.6352\pythonFiles\lib\python\ptvsd\_vendored\pydevd\pydevd.py", line 1024, in process_internal_commands
    int_cmd.do_it(self)
  File "c:\Users\test\.vscode\extensions\ms-python.python-2019.3.6352\pythonFiles\lib\python\ptvsd\_vendored\pydevd\_pydevd_bundle\pydevd_comm.py", line 485, in do_it
    self.method(dbg, *self.args, **self.kwargs)
  File "c:\Users\test\.vscode\extensions\ms-python.python-2019.3.6352\pythonFiles\lib\python\ptvsd\_vendored\pydevd\_pydevd_bundle\pydevd_comm.py", line 655, in internal_get_variable_json
    for child_var in variable.get_children_variables(fmt=fmt):
  File "c:\Users\test\.vscode\extensions\ms-python.python-2019.3.6352\pythonFiles\lib\python\ptvsd\_vendored\pydevd\_pydevd_bundle\pydevd_suspended_frames.py", line 108, in get_children_variables
    for key, val, evaluate_name in lst:
ValueError: need more than 2 values to unpack

Expected behavior

No exception, No debugging stops, Expand the list and show all items in the list.

Steps to reproduce:

See above.