Only assign a SymbolVersionAux to a SymbolVersion if it does not yet contain one.
Only assign a SymbolVersionAux to a SymbolVersion if it does not yet contain one.

This makes sure that whenever we have a SymbolVersionDefinition with multiple
entries only the first entry gets associated to the SymbolVersion.
Subsequent entries represent version predecessors, not the main version of the symbol
definition.

lief-project/LIEF,lief-project/LIEF,lief-project/LIEF,lief-project/LIEF