Prevent Mantid crash when fitting Gaussian peaks for a CrystalFieldFunction

[SilkeSchomann]

Description of work.

Added check for height ties based on sigma for Gaussian peaks within a CrystalFieldFunction to void IFunction::sortTies(). In this case the tie is not sorted but still applied as usual for its respective peak function. The sortTies function does not differentiate between ties applied to individual peaks separately and ties that can potentially influence each other. This caused Mantid crashes for multisite CrystalField objects with Gaussian peaks as Gaussian peaks automatically have a tie based on sigma for its height.

To test:

Run the script from the original issue 34245 and check it works.

Fixes #34245

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