[Bug] Dataset with timeseries data

### Version

6.0.0

### Link to Minimal Reproduction

https://echarts.apache.org/examples/en/editor.html?c=bar-simple&code=MYewdgzgLgBAJgQygiBTKBlEBXATsVGAXhgG0AoGMgckSlWoBoZqFcoBLYAG0IEYmLNpx6EATINbsuvGAGZqAXUaUaYgAxiArAFp1fPQOZ9165hrMww2bt2WrS1Ddr1jDgk33P7mc_fapHZ111OXdma1sIm25fUIC1TRCAFnCYE2ToqPl1ZMVyRQBucnJQSFg0XA5UCAARJARiMlUAb1UqKABPAAdUAC4WACM2JnarBABbfqFpUXTRqipoBGAAawHqCGwJgH0wdAXFugQBikXFoKTDNJN1BPPLl00b_xVzwKcr0LTIuzf3x4pF55Mb5KgAX3-bXOXV6G2GuEOVDAk2mUhEsgk_yWyDWGy2u32UCR8AapzGH2C130ggs9wunyebhp3j49MpXzCLKsMXZiSeqW5vzBixFkNaY1haIRJJRUw2whkhAU2JgyzxLAJewOquO5Pe_JCBiFvNVHKZaT8bLNhr0XKMOTkfMBekFDr8IPOYoKxVK4GgpOQaCgAHlupxwE1oTAAB4AQRjHAgAxaMClG04U2oMHFVE6CaTKdzMF4AHNUGA4EX_lAQCBuJxuim01VS-XcArExBBAguwAFEAcMD0DswVPpzUACwQcBAAHds-Cc_9jsGU2MIDh8NNV-gsHgCKrKtUIAAJVAz1CjqC4bCoVTF481fWLcc9aUjZjq9aa7ba4nLmMb5wkMn5qriP6bH-RKLqqwEfoiX4Qfi0EHDmqj5OCvplAGT51A0YYRmAUaqPGXbNhO1CZgwgF5gWyZjsWZYVlWjE1nWDYcE2Y4thwbZXp2SY9v2g7DgJPGURA06zguOa0WqV4ngMeH1Mg5BYSUAD0mlppOSYKagEwQGmIAwHOIC4Os5DaSA4YcJGJAqQRdngFpOlQHpxmzjUYBUX05C2URTS7qGLlgEAA

### Steps to Reproduce

I have an SQL data source, which gives me data in the following form:

```js
const sqlQuery = `
select generate_series::date as "date",
invoices.article_id,
sum(invoices.total_net) as sum_net
from generate_series('2025-01-01'::date, '2025-04-01'::date, '1 month'::interval)
join invoice_positions on date_trunc('month', invoice_positions.date) = generate_series::date
group by generate_series::date as date, invoices.article_id
`;

const sqlResult = [
['date', 'article_id', 'sum_net'],
['2025-01-01', 1, 100],
['2025-01-01', 2, 200],
['2025-01-01', 3, null],
['2025-02-01', 1, 101],
['2025-02-01', 2, 201],
['2025-02-01', 3, 301],
['2025-03-01', 1, null],
['2025-03-01', 2, null],
['2025-03-01', 3, 303],
['2025-04-01', 1, 104],
['2025-04-01', 2, null],
['2025-04-01', 3, 304]
];
```

After some processing, I currently transfer this data to the client:

```js
const fetchedData = {
columns: [
{ id: 'date', type: 'date' },
{ id: 'article_id', type: 'ref' },
{ id: 'sum_net', type: 'currency' }
],
rows: [
['2025-01-01', 1, 100],
['2025-01-01', 2, 200],
['2025-01-01', 3, null],
['2025-02-01', 1, 101],
['2025-02-01', 2, 201],
['2025-02-01', 3, 301],
['2025-03-01', 1, null],
['2025-03-01', 2, null],
['2025-03-01', 3, 303],
['2025-04-01', 1, 104],
['2025-04-01', 2, null],
['2025-04-01', 3, 304]
],
refs: {
article_id: [
[1, 'article 1'],
[2, 'article 2'],
[3, 'article 3']
]
}
};
```

Now, to chart this data, I have two options: Either make a `dataset`, or embed `data` in the series:

dataset.source

```js
const datasetSource = [
['date', 'article 1', 'article 2', 'article 3'],
['2025-01-01', 100, 200, null],
['2025-02-01', 101, 201, 301],
['2025-03-01', null, null, 303],
['2025-04-01', 104, null, 304]
];
```

series[i].data

```js
const seriesData = [
{
type: 'bar',
name: 'article 1',
stack: 'sum_net',
data: [
['2025-01-01', 100],
['2025-02-01', 101],
['2025-03-01', null],
['2025-04-01', 104]
]
},
{
type: 'bar',
name: 'article 2',
stack: 'sum_net',
data: [
['2025-01-01', 200],
['2025-02-01', 201],
['2025-03-01', null],
['2025-04-01', null]
]
},
{
type: 'bar',
name: 'article 3',
stack: 'sum_net',
data: [
['2025-01-01', null],
['2025-02-01', 301],
['2025-03-01', 303],
['2025-04-01', 304]
]
}
];
```

Since `dataset` seems to be specifically for tabular data, this option make sense to me, so I try to setup a chart like this:

```js
option = {
xAxis: { type: 'time' },
yAxis: {},
legend: {},
tooltip: { trigger: 'axis', axisPointer: { type: 'shadow' } },
dataset: {
source: datasetSource,
seriesHeader: true
},
series: [
{ type: 'bar', stack: 'sum_net' },
{ type: 'bar', stack: 'sum_net' },
{ type: 'bar', stack: 'sum_net' }
]
};
```

Using `xAxis: { type: "time" }` makes intuitively sense to me.

### Current Behavior

The generated graph looks wrong in multiple places:

1. The x axis starts at 1970-01-01
- Presumably, because some date is parsed as `null`/`NaN`, which get re-interpreted as `new Date(0)`. Not entirely sure.
2. The legend labels are pair-wise concatenated ("date article 1" and "article 2 article 3").
- I have no clue as to how this could have happened.

### Expected Behavior

Embedding the data in the series leads to the following graph:

Note:

1. The x axis correctly shows the months, and
2. The legend correctly shows three articles.

### Environment

```markdown
- OS: Debian 12 (that should not matter)
- Browser: Firefox 144.0, Chrome 141, Chrome 142 beta)
- Framework: none
```

### Any additional comments?

_No response_