Fix GH-8561: SplFileObject key()/current() desync after fgets()

fgets() read a line into the cache and incremented the line counter,
but left the cached line in place. The subsequent current() returned
the stale cached value instead of reading the next line from the
stream's actual position.

Clear the cached line after fgets() copies it to the return value.
This forces current() to re-read from the stream, which has already
advanced past the fgets'd line.

Closes GH-8561

Author: iliaal

ext/spl/spl_directory.c

@@ -2096,7 +2096,8 @@ PHP_METHOD(SplFileObject, fgets)
 	if (spl_filesystem_file_read_ex(intern, /* silent */ false, /* line_add */ 1, /* csv */ false) == FAILURE) {
 		RETURN_THROWS();
 	}
-	RETURN_STR_COPY(intern->u.file.current_line);
+	RETVAL_STR_COPY(intern->u.file.current_line);
+	spl_filesystem_file_free_line(intern);
 } /* }}} */
 
 /* {{{ Return current line from file */

ext/spl/tests/SplFileObject/gh8561.phpt

@@ -0,0 +1,30 @@
+--TEST--
+GH-8561 (SplFileObject: key() and current() unsynchronized after fgets())
+--FILE--
+<?php
+$file = new SplTempFileObject();
+for ($i = 0; $i < 5; $i++) {
+    $file->fwrite("line {$i}" . PHP_EOL);
+}
+
+// Case 1: rewind + fgets, then key/current
+$file->rewind();
+$file->fgets();
+echo "After rewind+fgets: key=" . $file->key() . " current=" . trim($file->current()) . "\n";
+
+// Case 2: multiple fgets
+$file->rewind();
+$file->fgets();
+$file->fgets();
+echo "After rewind+fgets+fgets: key=" . $file->key() . " current=" . trim($file->current()) . "\n";
+
+// Case 3: current then fgets
+$file->rewind();
+$file->current();
+$file->fgets();
+echo "After current+fgets: key=" . $file->key() . " current=" . trim($file->current()) . "\n";
+?>
+--EXPECT--
+After rewind+fgets: key=1 current=line 1
+After rewind+fgets+fgets: key=2 current=line 2
+After current+fgets: key=1 current=line 2