Always delete tempfile created by ftruncate test.

The ftruncate() test will fill up the disk when the disk has less than
2GB of space left, on some systems.
I think it expands the file to less than 2GB, then returns an error code,
and the file remains at the larger size.

Because the disk is full, the `--CLEAN--` script can't be saved to
`ftruncate_bug76422.clean.php` to be executed, and the cleanup can't be run.
Subsequent tests also fail to run.

Closes GH-5043

Author: TysonAndre

ext/standard/tests/file/ftruncate_bug76422.phpt

@@ -23,18 +23,26 @@ $truncate_offset = 2 * 1024 * 1024 * 1024;
 $ftruncate_result = ftruncate($file_handle, $truncate_offset);
 if (false === $ftruncate_result) {
     var_dump(true);
+    fclose($file_handle);
+    unlink($fn);
     return;
 }
 
 $truncate_offset = 4 * 1024 * 1024 * 1024 + 1;
 $ftruncate_result = ftruncate($file_handle, $truncate_offset);
 
 if (false === $ftruncate_result) {
+    // NOTE: unlink() is deliberately repeated - If this test runs out of disk space attempting to reserve space for this temporary file,
+    // then the --CLEAN-- script can't be run (if we don't delete the file),
+    // because there wouldn't be any free disk space to save a new php file.
+    fclose($file_handle);
+    unlink($fn);
     die('Truncate has failed :/');
 }
 
 fclose($file_handle);
 var_dump(filesize($fn) >= $truncate_offset);
+unlink($fn);
 ?>
 --CLEAN--
 <?php