Move dirty EOF handling to UTF-16

It remains useful for this encoding, which is other self-synchronizing

lib/Encoding/AbstractEncoding.php

@@ -17,8 +17,6 @@ abstract class AbstractEncoding implements Encoding {
     protected $lenByte = null;
     /** @var int $lenChar The length of the string in characters, if known */
     protected $lenChar = null;
-    /** To be removed */
-    protected $dirtyEOF = 0;
     /** @var array $errStack A list of error data to aid in backwards seeking; the most recent error is kept off the stack */
     protected $errStack = [];
     /** @var int $errMark The byte position marking the most recent error. The one or more bytes previous to this position constitute an invalid character */
@@ -89,13 +87,6 @@ abstract class AbstractEncoding implements Encoding {
             if (!$this->posChar) {
                 return $distance;
             }
-            if ($this->dirtyEOF > 0) {
-                // if we are at the end of the string and it did not terminate cleanly, go back the correct number of dirty bytes to seek through the last character
-                $this->posByte -= $this->dirtyEOF;
-                $this->dirtyEOF = 0;
-                $distance--;
-                $this->posChar--;
-            }
             $mode = $this->errMode;
             $this->errMode = self::MODE_NULL;
             $out = $this->seekBack($distance);

lib/Encoding/UTF16.php

@@ -8,6 +8,7 @@ namespace MensBeam\Intl\Encoding;
 
 abstract class UTF16 extends AbstractEncoding {
     protected $selfSynchronizing = true;
+    protected $dirtyEOF = 0;
 
     public function nextCode() {
         $lead_b = null;
@@ -80,6 +81,12 @@ abstract class UTF16 extends AbstractEncoding {
 
     /** Implements backward seeking $distance characters */
     protected function seekBack(int $distance): int {
+        if ($this->dirtyEOF && $distance) {
+            $distance--;
+            $this->posChar--;
+            $this->posByte -= $this->dirtyEOF;
+            $this->dirtyEOF = 0;
+        }
         while ($distance > 0 && $this->posByte > 0) {
             $distance--;
             $this->posChar--;