[patch] syncdb initial sql data regexp breaks if empty string is inserted

[Steven Armstrong]

The regexp sql_expr in management.py:get_sql_initial_data_for_model breaks if the inital sql data inserts empty strings.

e.g. in the sql below, the inserts for field2 and field3 break.

insert into mytable (field1, field2, field3) values ('bla', '', "");

The attached patch fixes that.

[Adrian Holovaty]

(In [3003]) Fixed #2015 -- Fixed sqlinitialdata regexp to handle empty string insertions. Thanks, Steven Armstrong