[BUG] Unchecked fopen() and alloc_demuxer_data() return values in process_hex() in general_loop.c

[Navdeepkaur-11]

Summary

In process_hex() in src/lib_ccx/general_loop.c, two return
values are not checked:

1. fopen() on line 370 — if the file cannot be opened, fr
   is NULL and the subsequent fgets(fr) call will crash
   with a segfault.

2. alloc_demuxer_data() on line 374 — return value is never
   checked. If allocation fails, data will be NULL and cause
   undefined behavior when used later.

Code

FILE *fr = fopen(filename, "rt");  // ← no NULL check
// ...
struct demuxer_data *data = alloc_demuxer_data();  // ← no NULL check
while (fgets(line, max - 1, fr) != NULL)  // ← crashes if fr is NULL

Suggested Fix

Add NULL checks for both with appropriate fatal() calls,
freeing already-allocated resources before exiting.