TypeError fix for unexpected NoneType in list

FIX: TypeError: unsupported operand type(s) for +: 'int' and 'NoneType'

Caused when the "finished" list is summed with the function "sum".

speedtest.py

@@ -1656,6 +1656,7 @@ class Speedtest(object):
                 while _is_alive(thread):
                     thread.join(timeout=0.001)
                 in_flight['threads'] -= 1
+                if type(thread.result) in (int, float):
                     finished.append(thread.result)
                 callback(thread.i, request_count, end=True)