StatesCurrentDiscoverCmd and StatesDesiredDiscoverCmd should include an entry for each item spec, even if the state cannot be looked up

[azriel91]

Steps to reproduce

1. Run StatesDiscoverCmd for a Flow, where an item spec's current / desired state cannot be looked up due to a predecessor state not being available.

Expected outcome

The number of states presented matches the number of item specs in the graph, and hence is always consistent.

Actual outcome

Item specs' whose state cannot be discovered are not listed:

<!-- 4 current states -->
1. `iam_policy`: does not exist
2. `iam_role`: does not exist
3. `web_app_download`: `azriel91/web_app/0.1.1/web_app.tar` non-existent, ETag not yet determined
4. `web_app_extract`: 0 files

<!-- 3 desired states -->
1. `iam_policy`: /dev policy should exist
2. `iam_role`: /dev role should exist
3. `web_app_download`: `azriel91/web_app/0.1.1/web_app.tar` containing 6492160 bytes, ETag: "0x8DAEA1931AF89EE"

The web_app_extract desired state is not listed as it cannot determine how many files are in the tar file which has not been downloaded.