e2fsck: fix free pointer dereferences

Commit 47fee2ef6a23a introduces some free pointer dereference bugs by
not clearing ctx->fs after calling ext2fs_close_free().

Reported-by: Matthias Andree <mandree@FreeBSD.org>
Cc: Lukas Czerner <lczerner@redhat.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
resize2fs: fix fs->blocksize dereference after fs has been freed

Commit 77255cf36944b introduced a use after free bug.

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