CVE-2026-11822: fix memory corruption in FTS5 fts5LeafRead() by rejecting
leaf pages with szLeaf < 4, blocking the OOB read in fts5LeafSeek()
CVE-2026-11824: fix heap-based buffer overflow via integer underflow in
fts5ChunkIterate() when szLeaf < 4 (same root cause; closed by the same
fts5LeafRead validation tightening)