Fix bug in BitWriter::WriteMultiple. (libjxl#4027)

Fixes libjxl#4026.

lib/jxl/enc_fast_lossless.cc

@@ -279,7 +279,7 @@ struct BitWriter {
         this->bits_in_buffer += nbits[i];
         // This `if` seems to be faster than using ternaries.
         if (this->bits_in_buffer >= 64) {
-          uint64_t next_buffer = bits[i] >> shift;
+          uint64_t next_buffer = shift >= 64 ? 0 : bits[i] >> shift;
           this->buffer = next_buffer;
           this->bits_in_buffer -= 64;
           this->bytes_written += 8;