Throw exception when trying to load unsupported schematics

[ColinHDev]

If a schematic is loaded from a file, there is no error thrown if the schematic version is greater than the one supported by that CPlot instance.

Currently, this was never a problem, since the latest schematic version has been around since nearly the beginning. But CPlot for PM5 introduces a new schematic version. Any server trying to load such a schematic on a PM4 server would not notice this until empty roads would start to appear.

[ColinHDev]

Fixed in c21a39e2d68262567c6c7065611a33484a2312ee