Bug report

Bug summary

The polygon perimeter created by hist() with histtype='stepfilled' in
combination with a non-None bottom argument has an invalid starting point.
This leads to a skewed lower edge of the first bin.

Code for reproduction

import matplotlib.pyplot as plt

# Data
data = [0, 0, 1, 1, 1]

# Bin edges
bins = [0, 1, 2]

plt.hist(data,
         bins=bins,
         bottom=[1, 2],  # Set lower edge
         histtype='stepfilled')

plt.savefig("example.png")

Actual outcome

Expected outcome

The lower left point of the first bin should at coordinates (0, 1).

Matplotlib version

• Operating system: Debian (python:3.7 Docker image)
• Matplotlib version: 3.1.2
• Matplotlib backend (print(matplotlib.get_backend())): agg
• Python version: 3.7.5
• matplotlib installed via pip