[FIX] Add NULL checks for fopen() and alloc_demuxer_data() in process_hex() (#2202)

* fix(general_loop): Add NULL checks for fopen() and alloc_demuxer_data() in process_hex()

* docs: update changelog for process_hex NULL checks fix

* fix: use EXIT_READ_ERROR for fopen failure and remove CHANGES.TXT entry

Author: Navdeepkaur-11

src/lib_ccx/general_loop.c

@@ -368,10 +368,19 @@ void process_hex(struct lib_ccx_ctx *ctx, char *filename)
 	}
 	/* const char *mpeg_header="00 00 01 b2 43 43 01 f8 "; // Always present */
 	FILE *fr = fopen(filename, "rt");
+	if (!fr)
+	{
+		fatal(EXIT_READ_ERROR, "In process_hex: Unable to open file %s for reading.", filename);
+	}
 	unsigned char *bytes = NULL;
 	unsigned byte_count = 0;
 	int warning_shown = 0;
 	struct demuxer_data *data = alloc_demuxer_data();
+	if (!data)
+	{
+		fclose(fr);
+		fatal(EXIT_NOT_ENOUGH_MEMORY, "In process_hex: Out of memory allocating demuxer data.");
+	}
 	while (fgets(line, max - 1, fr) != NULL)
 	{
 		char *c1, *c2 = NULL; // Positions for first and second colons