MDL-36640 Logging: Correct testing of log->info.

log->info sometimes contains additional information which can be looked up
from other tables. This should only be attempted if the field is numeric,
but the CSV, XLS, and ODS outputs were not making this check.

There is an additional case for the print_mnet_log function which has not
been covered - this is because the mnet logging is currently broken beyond
the scope of this bug rendering this section untestable. These issues are
raised in MDL-36642.

course/lib.php

@@ -583,7 +583,7 @@ function print_log_csv($course, $user, $date, $order='l.time DESC', $modname,
             $ld = $DB->get_record('log_display', array('module'=>$log->module, 'action'=>$log->action));
             $ldcache[$log->module][$log->action] = $ld;
         }
-        if ($ld && !empty($log->info)) {
+        if ($ld && is_numeric($log->info)) {
             // ugly hack to make sure fullname is shown correctly
             if (($ld->mtable == 'user') and ($ld->field ==  $DB->sql_concat('firstname', "' '" , 'lastname'))) {
                 $log->info = fullname($DB->get_record($ld->mtable, array('id'=>$log->info)), true);
@@ -684,7 +684,7 @@ function print_log_xls($course, $user, $date, $order='l.time DESC', $modname,
             $ld = $DB->get_record('log_display', array('module'=>$log->module, 'action'=>$log->action));
             $ldcache[$log->module][$log->action] = $ld;
         }
-        if ($ld && !empty($log->info)) {
+        if ($ld && is_numeric($log->info)) {
             // ugly hack to make sure fullname is shown correctly
             if (($ld->mtable == 'user') and ($ld->field == $DB->sql_concat('firstname', "' '" , 'lastname'))) {
                 $log->info = fullname($DB->get_record($ld->mtable, array('id'=>$log->info)), true);
@@ -798,7 +798,7 @@ function print_log_ods($course, $user, $date, $order='l.time DESC', $modname,
             $ld = $DB->get_record('log_display', array('module'=>$log->module, 'action'=>$log->action));
             $ldcache[$log->module][$log->action] = $ld;
         }
-        if ($ld && !empty($log->info)) {
+        if ($ld && is_numeric($log->info)) {
             // ugly hack to make sure fullname is shown correctly
             if (($ld->mtable == 'user') and ($ld->field == $DB->sql_concat('firstname', "' '" , 'lastname'))) {
                 $log->info = fullname($DB->get_record($ld->mtable, array('id'=>$log->info)), true);