FIX - rasql OVERLAY returns incorrect results

[Bang Pham Huu]

`Import the two coverages (provided by OGC CITE WMS 1.3.0 tests) in ​attachment:

• Buildings: two small pink rectangles at the top right
• MapNeatline: the dark-red rectangle which covers Buildings

then check the query (WMS from OGC CITE: layers=Buildings,MapNeatline, hence rasql Buildings OVERLAY MapNeatline):

rasql -q 'SELECT ENCODE((  (  EXTEND ( scale( scale( scale( ( ( c1[0:894,0:814] ) ), [0:799, 0:320] )  [0:799, 61:259], [0:399, 0:199] ), [0:352, 0:199] ), [-23:376, 0:199] ) )  )   OVERLAY (  (  EXTEND ( scale( scale( scale( ( ( c0[0:894,0:814] ) ), [0:799, 0:399] )  [0:799, 0:399], [0:399, 0:199] ), [0:67, 0:61] ), [-230:169, -39:160] ) )  ) , "png", "{}") FROM Buildings AS c0, MapNeatline AS c1' --out file

• The result is incorrect as Buildings layer doesn't show at all and it is hidden by MapNeatline layer.
  • It should show two pink rectangles on the MapNeatline.