Investment Period being dropped in Simplify Network

Checklist

• I am running on an up-to-date pypsa-usa environment. Update via conda env update -f envs/environment.yaml

Issue exisits on what branch

Develop

The Issue

If I run a muti-horizon model, but for only a subset of the year (ie. Jan and Feb) the workflow fails (I do acknowledge this is kinda an odd thing to run, haha)

Steps To Reproduce

Put this in the config file

# docs :
scenario:
  interconnect: ["western"] #"usa|texas|western|eastern"
  clusters: [80]
  opts: [Ep-Co2L0.2]
  ll: [v1.0]
  scope: "total" # "urban", "rural", or "total"
  sector: "" # G
  planning_horizons:
  - 2030
  - 2050 #(2030, 2040, 2050)

foresight:  # Only Single Stage Currently

# docs :
enable:
  build_cutout: false

snapshots:
  start: "2019-01-01"
  end: "2019-03-01"
  inclusive: "left"

Expected Behavior

No response

Error Message

INFO:pypsa.io:Imported network elec_s.nc has buses, carriers, generators, lines, links, loads, storage_units
Traceback (most recent call last):
  File "/home/trevor/repos/pypsa-usa/workflow/.snakemake/scripts/tmp7xtms1lm.cluster_network.py", line 512, in <module>
    n.snapshot_weightings.loc[n.investment_periods[0]].objective.sum() / 8760.0
                              ~~~~~~~~~~~~~~~~~~~~^^^
  File "/home/trevor/miniforge3/envs/pypsa-usa/lib/python3.11/site-packages/pandas/core/indexes/base.py", line 5389, in __getitem__
    return getitem(key)
           ^^^^^^^^^^^^
IndexError: index 0 is out of bounds for axis 0 with size

Anything else?

No response

Reproduce the provided multi-horizon configuration with January and February snapshots, then inspect the generated cluster_network.py around line 512 and the handling of n.investment_periods. Done means the workflow completes for this subset-year configuration without the IndexError and retains the expected investment period.