segfault in ogr.input when reading gpx lines with empty geoms - either tracks or routes layer

[artemp]

segfault on mac osx and ubuntu with both lines and multilines given the test with emtpy geoms here:

http://mapnik-utils.googlecode.com/svn/example_code/gpx_points_lines/

[artemp]

[springmeyer] Ah ha.

fixed in r1074

by checking for isEmpty rather than NULL:

http://www.gdal.org/ogr/classOGRGeometry.html#c8653ba97e53f3e3b041946ca2acc111