fix: add identifier validation to inc()

[mbtools]

• Adds a check of the identifier parameter for inc() when trying to increase pre-releases. This prevents the creation of an invalid semver.
• Removes side-effects of inc() when it is throwing (it was changing the version)

Closes #349

[wraithgar]

The .inc docs already state or null if it's not valid. This is how folks currently will have been building their code. We can't start throwing here w/o a semver major change.

We'll have to return null in cases where we're throwing in this PR. I do think refusing to generate invalid results is a good bugfix. Semver.inc('1.1.1', 'prerelease', 'dev/bar') should return null

[mbtools]

The inc() function does exactly that:

https://github.com/npm/node-semver/blob/main/functions/inc.js#L16

The classes usually throw if something is off. Should this be different here?

[wraithgar]

The inc() function does exactly that:

Ah yep you're right.