General: Correctly detect trailing newline when prepending.

We need to check that the final line is actually an artifact of explode(), not just an empty input string.

See #37082.


git-svn-id: https://develop.svn.wordpress.org/trunk@39592 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/pomo/po.php

@@ -169,7 +169,7 @@ class PO extends Gettext_Translations {
 	public static function prepend_each_line($string, $with) {
 		$lines = explode("\n", $string);
 		$append = '';
-		if ('' === end($lines)) {
+		if ("\n" === substr($string, -1) && '' === end($lines)) {
 			// Last line might be empty because $string was terminated
 			// with a newline, remove it from the $lines array,
 			// we'll restore state by re-terminating the string at the end