Fix GH-17399: iconv memory leak with large line-length

Move the buf allocation in _php_iconv_mime_encode() before the
iconv_open() calls. When max_line_len is excessively large (e.g.
PHP_INT_MAX), safe_emalloc triggers an OOM bailout that skips
cleanup, leaking the iconv handles allocated via system malloc.
By allocating buf first, a bailout happens before any iconv
handles exist.

Closes GH-17399

Author: iliaal

ext/iconv/iconv.c

@@ -942,6 +942,8 @@ static php_iconv_err_t _php_iconv_mime_encode(smart_str *pretval, const char *fn
 		goto out;
 	}
 
+	buf = safe_emalloc(1, max_line_len, 5);
+
 	cd_pl = iconv_open(ICONV_ASCII_ENCODING, enc);
 	if (cd_pl == (iconv_t)(-1)) {
 		if (errno == EINVAL) {
@@ -962,8 +964,6 @@ static php_iconv_err_t _php_iconv_mime_encode(smart_str *pretval, const char *fn
 		goto out;
 	}
 
-	buf = safe_emalloc(1, max_line_len, 5);
-
 	char_cnt = max_line_len;
 
 	_php_iconv_appendl(pretval, fname, fname_nbytes, cd_pl);

ext/iconv/tests/gh17399.phpt

@@ -0,0 +1,13 @@
+--TEST--
+GH-17399 (iconv memory leak with large line-length in iconv_mime_encode)
+--EXTENSIONS--
+iconv
+--FILE--
+<?php
+$options = array(
+    'line-length' => PHP_INT_MAX,
+);
+iconv_mime_encode('Subject', 'test', $options);
+?>
+--EXPECTF--
+Fatal error: Allowed memory size of %d bytes exhausted %s in %s on line %d