avoid potential zero division error (floating point exception) if image width and heigh == 0 (likely to happen when layer srs = 4326 and map srs = 900913) - see also #527 - avoid gdal crash on 'ERROR 1: The buffer into which the data should be read is null'

plugins/input/gdal/gdal_featureset.cpp

@@ -26,7 +26,7 @@
 
 // boost
 #include <boost/format.hpp>
-
+#define MAPNIK_DEBUG
 using mapnik::query;
 using mapnik::coord2d;
 using mapnik::Envelope;
@@ -156,6 +156,8 @@ feature_ptr gdal_featureset::get_feature(mapnik::query const& q)
           im_height = height;
       }
 
+      if (im_width > 0 && im_height > 0)
+      {
           mapnik::ImageData32 image(im_width, im_height);
           image.set(0xffffffff);
              
@@ -295,6 +297,7 @@ feature_ptr gdal_featureset::get_feature(mapnik::query const& q)
           }
           return feature;
       }
+   }
    return feature_ptr();
 }