Python event log analyzer tool: fix of indexing issue.

Test added to ensure it doesn't happen again.

NOTRY=True

Review-Url: https://codereview.webrtc.org/2316573003
Cr-Commit-Position: refs/heads/master@{#14121}

webrtc/tools/py_event_log_analyzer/rtp_analyzer.py

@@ -280,7 +280,7 @@ def calculate_delay(start, stop, step, points):
   masked array, in which time points with no value are masked.
 
   """
-  grouped_delays = [[] for _ in numpy.arange(start, stop, step)]
+  grouped_delays = [[] for _ in numpy.arange(start, stop + step, step)]
   rounded_value_index = lambda x: int((x - start) / step)
   for point in points:
     grouped_delays[rounded_value_index(point.real_send_time_ms)