Fix a bug mentioned in the last commit

The bug was that the wrong limb was set to the value.

Signed-off-by: Gavin D. Howard <gavin@gavinhoward.com>
diff --git a/src/num.c b/src/num.c
index be0d575..2e32ce7 100644
--- a/src/num.c
+++ b/src/num.c
@@ -3890,7 +3890,7 @@
 		// last limb is 0.
 		else
 		{
-			b->num[i] = (BcDig) bc_rand_bounded(rng, BC_BASE_POW);
+			b->num[i - 1] = (BcDig) bc_rand_bounded(rng, BC_BASE_POW);
 			b->len = atemp.len - 1;
 		}
 	}