libext2fs: Fix resize inode creation with non-standard s_first_data_block

libext2fs: Fix resize inode creation with non-standard s_first_data_block

Thanks to Max Lindner (lokimuh) for pointing this out.

   I'm playing around a bit with ext2 and multi-user encryption and I
   need space for my key management. So I set s_first_data_block to 4000
   or something like that.

   This way mke2fs segfaults when executing
   ext2fs_create_resize_inode() because

   blk_t goal = 3 + sb->s_reserved_gdt_blocks + fs->desc_blocks +
   fs->inode_blocks_per_group;

   will produce a integer underrun later and segfault then in the
   ext2fs_test_bit assembler inline function.

   when exchanging 3 with 2 + sb->s_first_data_block, mke2fs does not
   segfault.

   I'm not 100% sure if thats the correct way dealing with this issue
   but I think its a proper solution.

Addresses-Sourceforge-Bug: #1935847

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>