Fix legacy conversion filter for CP50220

Author: alexdowad

ext/mbstring/libmbfl/filters/mbfilter_cp5022x.c

@@ -338,7 +338,11 @@ static int mbfl_filt_conv_wchar_cp50220(int c, mbfl_convert_filter *filter)
 	if (filter->cache) {
 		int s = mbfl_convert_kana(filter->cache, c, &consumed, NULL, mode);
 		filter->cache = consumed ? 0 : c;
+		/* Terrible hack to get CP50220 to emit error markers in the proper
+		 * position, not reordering them with subsequent characters */
+		filter->filter_function = mbfl_filt_conv_wchar_cp50221;
 		mbfl_filt_conv_wchar_cp50221(s, filter);
+		filter->filter_function = mbfl_filt_conv_wchar_cp50220;
 	} else if (c == 0) {
 		/* This case has to be handled separately, since `filter->cache == 0` means
 		 * no codepoint is cached */

ext/mbstring/tests/cp5022x_encoding.phpt

@@ -375,6 +375,13 @@ $converted = mb_convert_encoding("ab\x00", 'UTF-16BE', 'CP50220');
 if ($converted !== "\x00a\x00b\x00\x00")
   die("Bad handling of trailing null byte (got " . bin2hex($converted) . ")");
 
+// Previously, the CP50220 implementation would reorder error markers with
+// subsequent characters
+mb_substitute_character(0x3F);
+$converted = mb_convert_encoding("\xff\xff\x00&", 'CP50220', 'UTF-16BE');
+if ($converted !== '?&')
+  die("Bad handling of erroneous codepoint followed by good one (got " . bin2hex($converted) . ")");
+
 ?>
 --EXPECT--
 ASCII support OK