Petascope_WMS should not use extend before scaling when generating Rasql query

[Bang Pham Huu]

For a coverage with a small footprint but the WMS clients send a request with much bigger footprint then Petascope will generate a rasql like this one:

SELECT ENCODE( ( Scale( 
Extend( ( ( c0[0:666, 0:440] ) ), [-72938:18013,-90511:440]), 
[0:255, 0:255] ) ) , "png", "{\"nodata\": [0,0,0,0]}") FROM cetvrto_polje_pyramid_32 as c0

The extend is the main problem and need to find a way to scale the selected grid domains ([0:666, 0:440]) as a portion of calculated extend ([-72938:18013, -90511:440]) based on the size of tiling (256 x 256), then extend this result to the size of tiling (256 x 256).