issue in StringList serialization

[esseffe]

I've noticed an issue in OGRFeature::GetFieldAsString()

when a StringList value is exported, the following serialized notation is adopted:

- value#1 = "A01"
- value#2 = "B02"
- serialized = "(2:A01,B01)"

this serialized format is generally fine (and is easily parsable by other apps), but will introduce fatal ambiguities when any COMMA is used by some value to be serialized:

- value#1 = "A,01"
- value#2 = "B,02"
- serialized = "(2:A,01,B,01)"

quite obviously, a serialized value like this can never be succesfully parsed so to retrieve the initial values.

suggested remedy: applying the same criteria used to mask quotes in SQL string, i.e. masking any COMMA found in the string value to be exported as COMMA-COMMA. This would produce the following output:

- value#1 = "A,01"
- value#2 = "B,02"
- serialized = "(2:A,,01,B,,01)"

a serialized string like this has no longer any ambiguity at all; and can be easily and safely parsed so to retrieve the original values.

please see the attached patch

best regards, Sandro Furieri