front: spacetimechart: fix drag behaviour when draging train to the left

[Math-R]

close #10511

Previously when you were dragging the earliest train to the left, the spaceTimeChart window was sliding to the left.
Now the SpaceTimeChart window won't move anymore unless you stop the train drag and pan the window

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.83%. Comparing base (ecb261f) to head (71577b9).
Report is 5 commits behind head on dev.

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Additional details and impacted files

@@            Coverage Diff             @@
##              dev   #10625      +/-   ##
==========================================
- Coverage   81.85%   81.83%   -0.02%     
==========================================
  Files        1075     1073       -2     
  Lines      107172   107078      -94     
  Branches      728      728              
==========================================
- Hits        87726    87630      -96     
- Misses      19407    19409       +2     
  Partials       39       39              

Flag	Coverage Δ
editoast	74.24% <ø> (-0.01%)	⬇️
front	89.37% <100.00%> (-0.02%)	⬇️
gateway	2.18% <ø> (ø)
osrdyne	3.28% <ø> (ø)
railjson_generator	87.50% <ø> (ø)
tests	88.14% <ø> (ø)

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