floatingLabelText overlaps text in the field when text is invalid and no errorText is specified

```
 <TextField type='number' step='0.01' defaultValue={1} ref='critical' floatingLabelText='Critical ' />
```

When I type `ss` in the field, and move focus outside the field, the floatingLabel overlaps with ss.

When I type a number, it works.

The picture is the same as https://github.com/callemall/material-ui/issues/563
