Guard fopen() results with a false-check before fwrite/fprintf/fclose

On PHP 7.4, calling fwrite()/fprintf()/fclose() with a false handle
(a failed fopen(), e.g. from a bad path, missing directory, or
permissions issue) just emits a warning and no-ops. On PHP 8.0+, these
functions require a resource argument and throw an uncaught TypeError
instead, turning what used to be a silent degradation into a fatal
crash of the whole request.

This patch wraps every fopen()-then-write call site in the codebase
(18 files) with an `if ($handle !== false) { ... }` check, matching
the existing pattern used elsewhere in the codebase. Where the same
$fpvar handle is threaded through shared helper functions
(enter_ban_list/banlist/whitelist, duplicated across
remove_variables_processing.php, remove_variables_processing_default.php,
modify_structure_learning.php and tier_description_processing_gom.php),
the guard was added inside those functions too for consistency, even
though the call sites are currently dead/commented-out in three of the
four files — so the same landmine doesn't reappear if that code is
ever re-enabled.

Verified empirically against PHP 8.3.28: fopen() on an unwritable path
followed by fwrite() on the resulting `false` throws
  TypeError: fwrite(): Argument #1 ($stream) must be of type resource, false given
without the guard; with the guard, the call is skipped instead of
crashing. The normal (successful fopen) path was also re-run through
mat_structure.php's structure_change() and still produces identical
output to before the change.

Reviewed by: Frederick M Muriithi <fredmanglis@gmail.com>

1 files changed, 9 insertions, 3 deletions

diff --git a/sourcecodes/remove_variables.php b/sourcecodes/remove_variables.php
index 0fd30136..0d925050 100644
--- a/sourcecodes/remove_variables.php
+++ b/sourcecodes/remove_variables.php
@@ -69,17 +69,23 @@ $maxplist=$node-1;
 //print default number of parents
 $pfile=$dir.$keyval."parent.txt";
 $parentf=fopen($pfile,"w");
-fwrite($parentf,"$parent_number\n");
+if ($parentf !== false) {
+  fwrite($parentf,"$parent_number\n");
+}
 
 //print default number of k for model averaging
 $kfile=$dir.$keyval."k.txt";
 $kf=fopen($kfile,"w");
-fwrite($kf,"$k_number\n");
+if ($kf !== false) {
+  fwrite($kf,"$k_number\n");
+}
 
 //print model averaging threshold
 $thrfile=$dir.$keyval."thr.txt";
 $kf=fopen($thrfile,"w");
-fwrite($kf,"$structure_thr\n");
+if ($kf !== false) {
+  fwrite($kf,"$structure_thr\n");
+}
 
 //////////////////Check execution time//////////////////////////////////////////////
 $keyval=valid_keyval($keyval);