erofs: validate the extent length for uncompressed pclusters

In the Linux kernel, the following vulnerability has been resolved: erofs: validate the extent length for uncompressed pclusters syzkaller reported a KASAN use-after-free: https://syzkaller.appspot.com/bug?extid=2ae90e873e97f1faf6f2 The referenced fuzzed image actually has two issues: - m_pa == 0 as a non-inlined pcluster; - The logical length is longer than its physical length. The first issue has already been addressed. This patch addresses the second issue by checking the extent length validity.