Fix condition; remove unreachable panic.

random.go

@@ -78,7 +78,7 @@ func randomBytesMod(length int, mod byte) (b []byte) {
 	for {
 		r := randomBytes(length + (length / 4))
 		for _, c := range r {
-			if c >= maxrb {
+			if c > maxrb {
 				// Skip this number to avoid modulo bias.
 				continue
 			}
@@ -89,7 +89,6 @@ func randomBytesMod(length int, mod byte) (b []byte) {
 			}
 		}
 	}
-	panic("unreachable")
 }
 
 // randomId returns a new random id string.