Issue 2193 starting solution

[valentinsulzer]

Description

Fixes bug with starting solution, which gave different solutions when running an experiment multiple times

(can wait until the next release, will update changelog after)

Fixes #2193

Type of change

Please add a line in the relevant section of CHANGELOG.md to document the change (include PR #) - note reverse order of PR #s. If necessary, also add to the list of breaking changes.

• New feature (non-breaking change which adds functionality)
• Optimization (back-end change that speeds up the code)
• Bug fix (non-breaking change which fixes an issue)

Key checklist:

• No style issues: $ flake8
• All tests pass: $ python run-tests.py --unit
• The documentation builds: $ cd docs and then $ make clean; make html

You can run all three at once, using $ python run-tests.py --quick.

Further checks:

• Code is commented, particularly in hard-to-understand areas
• Tests added that prove fix is effective or that feature works

[codecov]

Codecov Report

Merging #2204 (56cae9b) into develop (17cd564) will increase coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head 56cae9b differs from pull request most recent head 7bf7e42. Consider uploading reports for the commit 7bf7e42 to get more accurate results

@@           Coverage Diff            @@
##           develop    #2204   +/-   ##
========================================
  Coverage    99.36%   99.36%           
========================================
  Files          355      355           
  Lines        19506    19514    +8     
========================================
+ Hits         19382    19390    +8     
  Misses         124      124           

Impacted Files	Coverage Δ
pybamm/models/base_model.py	98.55% <100.00%> (+0.01%)	⬆️
pybamm/solvers/base_solver.py	100.00% <100.00%> (ø)
pybamm/experiments/experiment.py	100.00% <0.00%> (ø)
pybamm/meshes/one_dimensional_submeshes.py	100.00% <0.00%> (ø)

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[brosaplanella]

Looks good, thanks @tinosulzer!