Bar chart issue: Generates merged bar chart if we reduces width of zoom bar to its certain width.
Description:
1. Created bar chart with following given option object:
2. I reduced width of zoom bar to its certain width, as given in option object:  "minSpan": 0.5 
3. Have a look at attached screenshot.
```js
option = {
    xAxis: {
        type: 'category',
        data: ['Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun']
    },
    yAxis: {
        type: 'value'
    },
    series: [{
        data: [120, 200, 150, 80, 70, 110, 130],
        type: 'bar'
    }],
     "dataZoom": {
    "type": "slider",
    "show": true,
    "minSpan": 0.5,
    "filterMode": "empty",
    "start": 87.65476305836627,
    "end": 94.3056847654145,
    "xAxisIndex": [
      0
    ]
  },
};
```

Result:
![medha2](assets/apache__echarts-10173/001.png)
![medha1](assets/apache__echarts-10173/002.png)

## Relevant pre-fix discussion

### Issue #9882

#### Comment at 2019-01-31T17:33:44Z

Here's a gif that explains the issue better:

![2019-01-31 11 31 57](assets/apache__echarts-10173/003.gif)

#### Comment at 2019-03-26T17:59:54Z

This also affects stacked column charts

![2019-03-25_12 52 42](assets/apache__echarts-10173/004.gif)