Add tab for backward compatible

Author: youkidearitai

ext/mbstring/mbstring.c

@@ -6395,7 +6395,7 @@ static zend_string* mb_mime_header_decode(zend_string *input, const mbfl_encodin
 					p = temp;
 					/* Decoding of MIME encoded word was successful;
 					 * Try to collapse a run of whitespace */
-					if (p < e && (*p == '\n' || *p == '\r' || *p == ' ')) {
+					if (p < e && (*p == '\n' || *p == '\r' || *p == '\t' || *p == ' ')) {
 						do {
 							p++;
 						} while (p < e && (*p == '\n' || *p == '\r' || *p == '\t' || *p == ' '));

ext/mbstring/tests/gh20674.phpt

@@ -7,6 +7,19 @@ mbstring
 
 $subject = '=?us-ascii?Q?The_PH?=  =?us-ascii?Q?P_8.5?=';
 var_dump(mb_decode_mimeheader($subject));
+
+// mb_decode_mimeheader's backward compatible for TAB(\t)
+$subject = "=?us-ascii?Q?The_PH?=\t=?us-ascii?Q?P_8.5?=";
+var_dump(mb_decode_mimeheader($subject));
+
+$subject = "=?us-ascii?Q?The_PH?=\t =?us-ascii?Q?P_8.5?=";
+var_dump(mb_decode_mimeheader($subject));
+
+$subject = "=?us-ascii?Q?The_PH?= \t =?us-ascii?Q?P_8.5?=";
+var_dump(mb_decode_mimeheader($subject));
 ?>
 --EXPECTF--
 string(11) "The PHP 8.5"
+string(11) "The PHP 8.5"
+string(11) "The PHP 8.5"
+string(11) "The PHP 8.5"