Problem in the GUI : the code can add twice the same scalar name

Hi,

In the "species transport" panel, if the user:
- add scalar1 then scalar2 and then scalar3
- then the user changes the name of scalar2 to scalar4 to have : scalar1, scalar4, scalar3
- and now the user adds a new scalar, the new scalar is scalar4 to have: scalar1, scalar4, scalar3 and scalar4.

I didn't take the time to find a fast smart correction to fix it.

Regards,

Yohann

Start at the species transport panel and reproduce the sequence of adding scalar1, scalar2, and scalar3, renaming scalar2 to scalar4, then adding another scalar. Trace how the panel chooses a new scalar name; done means the new name is unique and the listed scalars remain scalar1, scalar4, scalar3, and a distinct new scalar.

Written by the indexing model from the issue text.