Reset bit pos only if it was max

This allows custom use by moving the start of bit reading.

bit-buffer.c

@@ -120,6 +120,7 @@ bb_read (struct BIT_BUFFER *buffer, int size)
           if (!(fread (&(buffer->bits), sizeof (byte), 1, buffer->fp)))
             return NULL;
           buffer->first_read = 1;
+          if (buffer->pos == BYTE_BIT)
             buffer->pos = 0;
         }