Fix broken laplam

[pmarguinaud]

This branch demonstrate that laplam (biFourier encoding) is now broken and suggests a correction.

[FussyDuck]

All committers have signed the CLA.

[shahramn]

Thank you. There was one little mistake which valgrind uncovered.
In the file tests/grib_lam_bf.c, I had to change:

-    trunc[2].subnmsmax = NSTRON;
+    trunc[1].subnmsmax = NSTRON;