Add invalid branch distance error checking on BBC/BBS opcodes

[KungFuFurby]

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This merge request closes #219.

[KungFuFurby]

If you're wondering why my build failed on the pull request, clang was the cause, and a timeout error seems to have been the cause (specifically, while uploading asar.dll): Error uploading artifact to the storage: Unable to read data from the transport connection: The connection was closed.

[trillllian]

note: i deleted the foundlabel check your commit had. if the subtraction is unconditional, the overflow checking should be too. whether it should be unconditional is a different issue...