Set capacity to length before storing value

So I think we can state that the bugs we have in gnolang#960, gnolang#1167 and gnolang#1170,
are all related to slice storage when its capacity is different than its
length.

@deelawn found a great way to overcome that bug, but the bug is still
there, somewhere in the VM code I think. I spent the last couple of days
trying to find it, unfortunately without success.

That said, I found a workaround, that could be also applied: when a
slice is stored, ignore any capacity different than the slice's length.

I think this is a good workaround because its one-line and because we
don't really care about storing slice with capacity higher than their
length (unless I'm missing something).

gnovm/pkg/gnolang/realm.go

@@ -1127,7 +1127,9 @@ func copyValueWithRefs(parent Object, val Value) Value {
 			Base:   toRefValue(parent, cv.Base),
 			Offset: cv.Offset,
 			Length: cv.Length,
-			Maxcap: cv.Maxcap,
+			// Force capacity to length, because we have issues with store when they
+			// are differents.
+			Maxcap: cv.Length,
 		}
 	case *StructValue:
 		fields := make([]TypedValue, len(cv.Fields))