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