MDL-44822 assignfeedback_editpdf: Stop test generation in is_enabled()

This change also moves one of the checks in test_gs_path. If
generateimage is false, there's no need to stat for the fixture file.

mod/assign/feedback/editpdf/classes/pdf.php

@@ -546,13 +546,13 @@ class pdf extends \FPDI {
             return $ret;
         }
 
-        $testfile = $CFG->dirroot.'/mod/assign/feedback/editpdf/tests/fixtures/testgs.pdf';
-        if (!file_exists($testfile)) {
-            $ret->status = self::GSPATH_NOTESTFILE;
+        if (!$generateimage) {
             return $ret;
         }
 
-        if (!$generateimage) {
+        $testfile = $CFG->dirroot.'/mod/assign/feedback/editpdf/tests/fixtures/testgs.pdf';
+        if (!file_exists($testfile)) {
+            $ret->status = self::GSPATH_NOTESTFILE;
             return $ret;
         }
 

mod/assign/feedback/editpdf/locallib.php

@@ -265,7 +265,7 @@ class assign_feedback_editpdf extends assign_feedback_plugin {
      * @return bool
      */
     public function is_enabled() {
-        $testpath = assignfeedback_editpdf\pdf::test_gs_path();
+        $testpath = assignfeedback_editpdf\pdf::test_gs_path(false);
         if (!extension_loaded('zlib')) {
             return false;
         }