Prevent dice overflow

rand.Int() would panic when the max value is <= 0, which happens when
big.NewInt() was fed with a too large number. Avoid this by validating
the big.NewInt() return beforehand. Add error handling to all callers to
both gracefully return to IRC and to log an error message.

Signed-off-by: Georg Pfuetzenreuter <mail@georg-pfuetzenreuter.net>

wat/game.go

@@ -2,6 +2,7 @@ package wat
 
 import (
 	"crypto/rand"
+	"errors"
 	"fmt"
 	"math/big"
 	"strconv"
@@ -121,11 +122,11 @@ func (g *WatGame) help() string {
 	return ret
 }
 
-func (g *WatGame) RandInt(maxx int64) (uint64, error) {
+func (g *WatGame) RandInt(max int64) (uint64, error) {
-	bi := big.NewInt(maxx)
+	bi := big.NewInt(max)
 	// prevent panic of rand.Int on big numbers
 	if bi.BitLen() < 2 {
-		return 0, fmt.Errorf("overflow, got %d", bi)
+		return 0, errors.New("overflow")
 	}
 	i, err := rand.Int(rand.Reader, bi)
 	if err != nil {