`dotnet workload install` with `--version` fails

[ManickaP]

If the provided version has less than 3 components, the command "crashes" with:

Workload installation failed: Index was outside the bounds of the array.

Looks like the parsing is broken and doesn't account well for human input:

sdk/src/Common/WorkloadSetVersion.cs

Lines 30 to 33 in d1b5a81

	string[] coreComponents = SeparateCoreComponents(workloadSetVersion, out string[] sections);
	string major = coreComponents[0];
	string minor = coreComponents[1];
	string patch = coreComponents[2];