Inconsitent index for plot
#### Code Sample
```python
import pandas as pd
import matplotlib.pyplot as plt

data = {"A":0, "B":3, "C":-4}
df = pd.DataFrame.from_dict(data, orient = "index", columns = ["Value"])
ax = df.plot.barh()

df = df.sort_values("Value") * - 2
df.plot.barh(ax = ax, color = "red")
plt.show()
```
#### Problem description
The second plot overwrites the first index even if it is not in the same order, producing incoherent figure where the ylabel does not match with the data displayed.
The current output (pandas 0.24.1) creates 
![current](https://user-images.githubusercontent.com/16624195/56530672-c762a380-6520-11e9-9330-07beba1aaea1.png)
instead of 
![correct](https://user-images.githubusercontent.com/16624195/56530671-c762a380-6520-11e9-8410-aa1789d1896e.png)

I don't know if this is related to the way pandas handles index or matplotlib.

