f2fs: fix to truncate first page in error path of f2fs_truncate()

In the Linux kernel, the following vulnerability has been resolved:

f2fs: fix to truncate first page in error path of f2fs_truncate()

syzbot reports a bug as below:

loop0: detected capacity change from 0 to 40427
F2FS-fs (loop0): Wrong SSA boundary, start(3584) end(4096) blocks(3072)
F2FS-fs (loop0): Can't find valid F2FS filesystem in 1th superblock
F2FS-fs (loop0): invalid crc value
F2FS-fs (loop0): f2fs_convert_inline_folio: corrupted inline inode ino=3, i_addr[0]:0x1601, run fsck to fix.
------------[ cut here ]------------
kernel BUG at fs/inode.c:753!
RIP: 0010:clear_inode+0x169/0x190 fs/inode.c:753
Call Trace:
<TASK>
evict+0x504/0x9c0 fs/inode.c:810
f2fs_fill_super+0x5612/0x6fa0 fs/f2fs/super.c:5047
get_tree_bdev_flags+0x40e/0x4d0 fs/super.c:1692
vfs_get_tree+0x8f/0x2b0 fs/super.c:1815
do_new_mount+0x2a2/0x9e0 fs/namespace.c:3808
do_mount fs/namespace.c:4136 [inline]
__do_sys_mount fs/namespace.c:4347 [inline]
__se_sys_mount+0x317/0x410 fs/namespace.c:4324
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

During f2fs_evict_inode(), clear_inode() detects that we missed to truncate
all page cache before destorying inode, that is because in below path, we
will create page #0 in cache, but missed to drop it in error path, let's fix
it.

- evict
- f2fs_evict_inode
- f2fs_truncate
- f2fs_convert_inline_inode
- f2fs_grab_cache_folio
: create page #0 in cache
- f2fs_convert_inline_folio
: sanity check failed, return -EFSCORRUPTED
- clear_inode detects that inode->i_data.nrpages is not zero