Fix BundleVersion comparison when short_version is not comparable

[khipp]

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This PR fixes an issue when comparing two BundleVersion objects where the version variables are equal and the short_version variables are nil. In this case, the result of the initial version comparison should be returned.

Before:

$ brew livecheck --cask teamviewer
Error: teamviewer: comparison of Array with Array failed

After:

$ brew livecheck --cask teamviewer
teamviewer: 15.58.4 ==> 15.58.4

[MikeMcQuaid]

Makes sense, thanks @khipp!