Fix dereference nullptr

[safocl]

some code contained nullptr dereferencing

calloc (in the mft_get_search_ctx function) can return nullptr, then need check and return nullptr? -- then m_ctx->flags_search is a nullptr dereferencing.

ntfs-3g/ntfsprogs/utils.c

Line 977 in 75dcdc2

ctx = (struct mft_search_ctx*)calloc(1, sizeof *ctx);