Fix GH-7980: Unexpected result for iconv_mime_decode

We need to reset the shift state right after conversion, to cater to
potenially following plain encodings.  Also, there is no need to reset
the shift for plain encodings, because these are not state-dependent.

Closes GH-8025.

NEWS

@@ -7,6 +7,7 @@ PHP                                                                        NEWS
 
 - Iconv:
   . Fixed bug GH-7953 (ob_clean() only does not set Content-Encoding). (cmb)
+  . Fixed bug GH-7980 (Unexpected result for iconv_mime_decode). (cmb)
 
 - Zlib:
   . Fixed bug GH-7953 (ob_clean() only does not set Content-Encoding). (cmb)

ext/iconv/iconv.c

@@ -1576,6 +1576,9 @@ static php_iconv_err_t _php_iconv_mime_decode(smart_str *pretval, const char *st
 						}
 
 						err = _php_iconv_appendl(pretval, ZSTR_VAL(decoded_text), ZSTR_LEN(decoded_text), cd);
+						if (err == PHP_ICONV_ERR_SUCCESS) {
+							err = _php_iconv_appendl(pretval, NULL, 0, cd);
+						}
 						zend_string_release_ex(decoded_text, 0);
 
 						if (err != PHP_ICONV_ERR_SUCCESS) {
@@ -1716,13 +1719,6 @@ static php_iconv_err_t _php_iconv_mime_decode(smart_str *pretval, const char *st
 		*next_pos = p1;
 	}
 
-	if (cd != (iconv_t)(-1)) {
-		_php_iconv_appendl(pretval, NULL, 0, cd);
-	}
-	if (cd_pl != (iconv_t)(-1)) {
-		_php_iconv_appendl(pretval, NULL, 0, cd_pl);
-	}
-
 	smart_str_0(pretval);
 out:
 	if (cd != (iconv_t)(-1)) {

ext/iconv/tests/gh7980.phpt

@@ -0,0 +1,13 @@
+--TEST--
+Bug GH-7980 (Unexpected result for iconv_mime_decode)
+--SKIPIF--
+<?php
+if (!extension_loaded("iconv")) die("skip iconv extension not available");
+?>
+--FILE--
+<?php
+$subject = '=?windows-1258?Q?DSI_Charg=E9_de_Formation_Jean_Dupont?= <jdupont@example.fr>';
+var_dump(iconv_mime_decode($subject, ICONV_MIME_DECODE_STRICT, 'UTF-8'));
+?>
+--EXPECT--
+string(57) "DSI Chargé de Formation Jean Dupont <jdupont@example.fr>"