Coding Standards: Fix instances of WordPress.PHP.NoSilencedErrors.Discouraged.

Noteable changes:
- The `magic_quotes_runtime` and `magic_quotes_sybase` settings were removed in PHP 5.4, so no longer need to be set.
- Some functions that use external libraries can generate errors that can't be tested for, so are globally allowed to silence errors.
- Quite a few functions would cause errors if `safe_mode` was set. This setting was removed in PHP 5.4.
- Only a handful of `header()` calls needed corresponding `headers_sent()` checks for unit tests to pass, but more may need to be added as the nightlies builds are tested.

See #46732.


git-svn-id: https://develop.svn.wordpress.org/trunk@45611 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/class-wp-image-editor-gd.php

@@ -436,7 +436,7 @@ class WP_Image_Editor_GD extends WP_Image_Editor {
 		// Set correct file permissions
 		$stat  = stat( dirname( $filename ) );
 		$perms = $stat['mode'] & 0000666; //same permissions as parent folder, strip off the executable bits
-		@ chmod( $filename, $perms );
+		chmod( $filename, $perms );
 
 		/**
 		 * Filters the name of the saved image file.