🐛 [BUG] Mix with multiple lines does not respect the x-coordinates in all of the data sources

### 🐛 Bug description [Please make everyone to understand it]

When using the mix plot and syncing axis' across plots, the data in the first plot determines the xAxis start point and disregards the xAxis in the data in the rest of the plots.

### 📷 Step to reproduce
[Minimal Reproduction(Sandbox)](https://codesandbox.io/s/g2plot-issue-template-forked-ott8sk?file=/index.ts)

### 🏞 Expected result
The expected result is that the coordinates in the xAxis of the two graphs is respected and the points are put in the right coordinate.

Start with the linked CodeSandbox reproduction in index.ts and compare how the mix plot synchronizes axes across its two data sources. Trace the mix plot axis handling to find why the first plot determines the x-axis start; done means both plots respect their x-coordinates and place points correctly.

Written by the indexing model from the issue text.