Check for overflow when calculating size of zip

src/extract.go

···
 	"errors"
 	"fmt"
 	"io"
+	"math"
 	"os"
 	"strings"
 
···
 	// Detect and defuse zipbombs.
 	var totalSize uint64
 	for _, file := range archive.File {
+		if totalSize+file.UncompressedSize64 < totalSize {
+			// Would overflow
+			totalSize = math.MaxUint64
+			break
+		}
 		totalSize += file.UncompressedSize64
 	}
 	if totalSize > config.Limits.MaxSiteSize.Bytes() {