Fix guard amount for invaderCore attacking

[schealex]

Pull request summary

Description:

amount was always zero because the invaderCore was not accounted for

Testing checklist:

• Changes are backward-compatible OR version migration code is included
• Codebase compiles with current tsconfig configuration
• Tested changes on {choose PUBLIC/PRIVATE} server OR changes are trivial (e.g. typos)

[MatthewARoy]

lgtm, the cores were getting cleaned up but I believe it was only when an invasion would spawn and trigger defense.

We should consider again splitting off this into a more efficient attack/move creep specializing in killing the cores, that was previously handled in the modular dismantle function.