do not leave empty dependencies

[perazz]

Motivation

fpm allocates the dependency array with additional space, that is left unused after the dependency tree is completed.

Because tree serialization creates an exact copy of the memory, the dependency toml/json may include several empty dependencies.

Specification

Always ensure that the dependency array has size(tree%deps) == tree%ndep after the dependency tree is built.
This will achieve no leftover empty dependencies with basically no performance penalty.

Prior Art

No response

Additional Information

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