Code cleanup of rt_raster_gdal_warp()

git-svn-id: http://svn.osgeo.org/postgis/trunk@11056 b70326c6-7e19-0410-871a-916f4a2858ee
Fix function parameter value overflow that caused problems when copying
data from a GDAL dataset. Problem first appeared in ST_Resize(). Ticket #2188

git-svn-id: http://svn.osgeo.org/postgis/trunk@11057 b70326c6-7e19-0410-871a-916f4a2858ee