Fix #55146: iconv_mime_decode_headers() skips some headers

If we're expecting the start of an encoded word (`=?`), but instead of
the question mark get a line break (CR or LF), we must not append it to
the `pretval`.

NEWS

@@ -13,6 +13,9 @@ PHP                                                                        NEWS
 - gettext:
   . Fixed bug #76517 (incorrect restoring of LDFLAGS). (sji)
 
+- iconv:
+  . Fixed bug #55146 (iconv_mime_decode_headers() skips some headers). (cmb)
+
 - intl:
   . Fixed bug #74484 (MessageFormatter::formatMessage memory corruption with
     11+ named placeholders). (Anatol)

ext/iconv/iconv.c

@@ -1555,6 +1555,9 @@ static php_iconv_err_t _php_iconv_mime_decode(smart_str *pretval, const char *st
 
 			case 1: /* expecting a delimiter */
 				if (*p1 != '?') {
+					if (*p1 == '\r' || *p1 == '\n') {
+						--p1;
+					}
 					err = _php_iconv_appendl(pretval, encoded_word, (size_t)((p1 + 1) - encoded_word), cd_pl);
 					if (err != PHP_ICONV_ERR_SUCCESS) {
 						goto out;

ext/iconv/tests/bug55146.phpt

@@ -0,0 +1,36 @@
+--TEST--
+Bug #55146 (iconv_mime_decode_headers() skips some headers)
+--SKIPIF--
+<?php
+if (!extension_loaded('iconv')) die('skip iconv extension not available');
+?>
+--FILE--
+<?php
+
+$headers = <<< HEADERS
+X-Header-One: H4sIAAAAAAAAA+NgFlsCAAA=
+X-Header-Two: XtLePq6GTMn8G68F0
+HEADERS;
+var_dump(iconv_mime_decode_headers($headers, ICONV_MIME_DECODE_CONTINUE_ON_ERROR));
+
+$headers = <<< HEADERS
+X-Header-One: =
+X-Header-Two: XtLePq6GTMn8G68F0
+HEADERS;
+var_dump(iconv_mime_decode_headers($headers, ICONV_MIME_DECODE_STRICT));
+?>
+===DONE===
+--EXPECT--
+array(2) {
+  ["X-Header-One"]=>
+  string(24) "H4sIAAAAAAAAA+NgFlsCAAA="
+  ["X-Header-Two"]=>
+  string(17) "XtLePq6GTMn8G68F0"
+}
+array(2) {
+  ["X-Header-One"]=>
+  string(1) "="
+  ["X-Header-Two"]=>
+  string(17) "XtLePq6GTMn8G68F0"
+}
+===DONE===