Illegal alias throws generic exception only

[elosha]

First, thank you for your super helpful macro! I love it.

Today I accidentally produced a situation in FreeCAD where one alias name suddenly became illegal, like I was trying to use an already taken name. However AliasManager only produced a very generic exception instead of telling me. Please add a more meaningful error message for this situation.

(When I tried to set the alias manually, FreeCAD signified with red text that the name was not allowed. So I found out the actual mistake …)

Specs:
FreeCAD 0.19-24366 (latest)
AliasManager latest