Removed illegal negative values to avoid overflow

Re-interpolated and removed illegal negative values to avoid overflow in Avisynth Cube() and DGCube() implementation. Credits to frank from Germany. For more info, see https://forum.doom9.org/showthread.php?p=1975710#post1975710

BT709_to_HLG.cube

@@ -1,7 +1,7 @@
 TITLE "BT709_to_HLG"
 LUT_3D_SIZE 65
 # BT709 SDR to BT2020 HLG with reference white 75% (Full Range in - Full Range out)
--0.00086043 -0.00046653 -0.00063309
+0.00819792 0.00242625 0.00043791
 0.00905835 0.00289278 0.00107100
 0.01858871 0.00607219 0.00265007
 0.02916544 0.00974503 0.00453822