When using the `map_from_region` for pen tables, we will usually make
the available area as big as possible while maintaining the proportions
with the screen.
As most of the tablets uses a 16:10 ratios while the most popular screen
ratios is still 16:9, the argument for most people should be `0x0 1x0.9`
to have the maximum effective area.
However, the argument above won't work because the current code will
treat `0x...` as a hexadecimal number, instead of setting both `x` and
`y` to `0`.
This fix allows the use of the following syntax:
```
input type:tablet_tool {
map_from_region 0x0 1x0.9
}
```
iff
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