Fix bug where transform_single_time_series! fails

[daniel-thom]

This function will throw an exception if the first component that has time series does not have any time series of type SingleTimeSeries.

[codecov[bot]]

Codecov Report

Merging #291 (41bf313) into master (04113c0) will decrease coverage by 0.01%. The diff coverage is 33.33%.

@@            Coverage Diff             @@
##           master     #291      +/-   ##
==========================================
- Coverage   78.28%   78.26%   -0.02%     
==========================================
  Files          43       43              
  Lines        3605     3456     -149     
==========================================
- Hits         2822     2705     -117     
+ Misses        783      751      -32     

Flag	Coverage Δ
unittests	78.26% <33.33%> (-0.02%)	:arrow_down:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/component.jl	94.05% <0.00%> (-0.23%)	:arrow_down:
src/system_data.jl	88.17% <50.00%> (-0.19%)	:arrow_down:
src/common.jl	66.66% <0.00%> (-33.34%)	:arrow_down:
src/utils/utils.jl	64.58% <0.00%> (-1.57%)	:arrow_down:
src/utils/print.jl	52.10% <0.00%> (-1.10%)	:arrow_down:
src/utils/generate_structs.jl	84.82% <0.00%> (-0.90%)	:arrow_down:
src/internal.jl	78.84% <0.00%> (-0.79%)	:arrow_down:
src/probabilistic.jl	77.19% <0.00%> (-0.78%)	:arrow_down:
src/scenarios.jl	83.67% <0.00%> (-0.65%)	:arrow_down:
src/deterministic.jl	81.53% <0.00%> (-0.56%)	:arrow_down:
... and 19 more