ktest: Avoid undef warning when WARNINGS_FILE is unset

check_buildlog() probes $warnings_file with -f even when WARNINGS_FILE is
not configured. Perl warns about the uninitialized value and adds noise to
the test log, which can hide the output we actually care about.

Check that WARNINGS_FILE is defined before testing whether the file exists.

Cc: John Hawley <[email protected]>
Cc: Andrea Righi <[email protected]>
Cc: Marcos Paulo de Souza <[email protected]>
Cc: Matthieu Baerts <[email protected]>
Cc: Fernando Fernandez Mancera <[email protected]>
Cc: Pedro Falcato <[email protected]>
Link: https://patch.msgid.link/[email protected]
Fixes: 4283b16 ("ktest: Add make_warnings_file and process full warnings")
Signed-off-by: Ricardo B. Marlière <[email protected]>
Signed-off-by: Steven Rostedt <[email protected]>

Author: rbmarliere

tools/testing/ktest/ktest.pl

@@ -2508,7 +2508,7 @@ sub check_buildlog {
     my $save_no_reboot = $no_reboot;
     $no_reboot = 1;
 
-    if (-f $warnings_file) {
+    if (defined($warnings_file) && -f $warnings_file) {
 	open(IN, $warnings_file) or
 	    dodie "Error opening $warnings_file";