ArcSDE provider: crash when using computed identifiers

[danstoica]

Use any computed identifier like Floor(numerical_property). A crash will occur.

This happens because when ArcSDEFeatureReader::PrepareStream () is storing the column names in an array of colums it doesn't take into account the fact sde_wide_to_multibyte () doesn't allocate memory and the result is a pointer to a volatile string. This string goes out of block scope and the array of columns contains garbage.