fsck.f2fs: check condition to avoid wrong memory allocation

fsck.f2fs: check condition to avoid wrong memory allocation

This patch should fix the below bug.

Info: checkpoint state = 4 :  compacted_summary sudden-power-off
[FIX] (is_valid_ssa_data_blk: 301)  --> Set data summary 0x1039 -> [0x3] [0x0] [0x0]
[ASSERT] (fsck_chk_data_blk:1459)  --> SIT bitmap is 0x0. blk_addr[0x20b6d8]
[ASSERT] (__chk_dentries:1255)  --> Bad dentry 0x2 with invalid NID/ino 0x1644b164
[FIX] (__chk_dentries:1258)  --> Clear bad dentry 0x2 with bad ino 0x1644b164
[ASSERT] (__chk_dentries:1269)  --> Bad dentry 0x0 with unexpected ftype 0x2c
[FIX] (__chk_dentries:1272)  --> Clear bad dentry 0x4 with bad ftype 0x2c
[ASSERT] (__chk_dentries:1255)  --> Bad dentry 0x5 with invalid NID/ino 0x49000000
[FIX] (__chk_dentries:1258)  --> Clear bad dentry 0x5 with bad ino 0x49000000
[ASSERT] (__chk_dentries:1255)  --> Bad dentry 0x7 with invalid NID/ino 0x67706a2e
[FIX] (__chk_dentries:1258)  --> Clear bad dentry 0x7 with bad ino 0x67706a2e
[ASSERT] (__chk_dentries:1255)  --> Bad dentry 0x8 with invalid NID/ino 0x4a437044
[FIX] (__chk_dentries:1258)  --> Clear bad dentry 0x8 with bad ino 0x4a437044
[ASSERT] (__chk_dentries:1269)  --> Bad dentry 0x0 with unexpected ftype 0x0
[FIX] (__chk_dentries:1272)  --> Clear bad dentry 0xf with bad ftype 0x0
[ASSERT] (__chk_dentries:1255)  --> Bad dentry 0x20 with invalid NID/ino 0x4a150009
[FIX] (__chk_dentries:1258)  --> Clear bad dentry 0x20 with bad ino 0x4a150009
[ASSERT] (__chk_dentries:1255)  --> Bad dentry 0x21 with invalid NID/ino 0x1800094a
[FIX] (__chk_dentries:1258)  --> Clear bad dentry 0x21 with bad ino 0x1800094a
*** buffer overflow detected ***: fsck.f2fs terminated
======= Backtrace: =========
/lib/x86_64-linux-gnu/libc.so.6(+0x7338f)[0x7fa56b17b38f]
/lib/x86_64-linux-gnu/libc.so.6(__fortify_fail+0x5c)[0x7fa56b212c9c]
/lib/x86_64-linux-gnu/libc.so.6(+0x109b60)[0x7fa56b211b60]
fsck.f2fs[0x4032f6]
fsck.f2fs[0x4063f7]
fsck.f2fs[0x406d09]
fsck.f2fs[0x4046b8]
fsck.f2fs[0x405378]
fsck.f2fs[0x405d86]
fsck.f2fs[0x402071]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf5)[0x7fa56b129ec5]

Reported-by: Mirh <mirh@protonmail.ch>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>