Code Modernization: Check if the file to retrieve metadata from in get_file_data() was successfully opened.

This avoids a fatal error on PHP 8 caused by passing a `false` value to `fread()`, instead of a file resource.

See #50913.

git-svn-id: https://develop.svn.wordpress.org/trunk@49073 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/functions.php

@@ -6040,11 +6040,15 @@ function get_file_data( $file, $default_headers, $context = '' ) {
 	// We don't need to write to the file, so just open for reading.
 	$fp = fopen( $file, 'r' );
 
+	if ( $fp ) {
 		// Pull only the first 8 KB of the file in.
 		$file_data = fread( $fp, 8 * KB_IN_BYTES );
 
 		// PHP will close file handle, but we are good citizens.
 		fclose( $fp );
+	} else {
+		$file_data = '';
+	}
 
 	// Make sure we catch CR-only line endings.
 	$file_data = str_replace( "\r", "\n", $file_data );