Refine fgets() to reuse cached line when present

When current() reads a line into the cache without advancing line_num,
a subsequent fgets() would re-read the stream and return the next line,
skipping the cached one and leaving key() out of sync with current()
for the rest of the iteration.

Use the cached line if present; otherwise read a fresh line. Either way,
advance line_num by one.

Author: iliaal

ext/spl/spl_directory.c

@@ -2096,11 +2096,17 @@ PHP_METHOD(SplFileObject, fgets)
 
 	CHECK_SPL_FILE_OBJECT_IS_INITIALIZED(intern);
 
-	if (spl_filesystem_file_read_ex(intern, /* silent */ false, /* line_add */ 1, /* csv */ false) == FAILURE) {
-		RETURN_THROWS();
+	if (intern->u.file.current_line) {
+		RETVAL_STR_COPY(intern->u.file.current_line);
+		spl_filesystem_file_free_line(intern);
+		intern->u.file.current_line_num++;
+	} else {
+		if (spl_filesystem_file_read_ex(intern, /* silent */ false, /* line_add */ 1, /* csv */ false) == FAILURE) {
+			RETURN_THROWS();
+		}
+		RETVAL_STR_COPY(intern->u.file.current_line);
+		spl_filesystem_file_free_line(intern);
 	}
-	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

@@ -27,4 +27,4 @@ echo "After current+fgets: key=" . $file->key() . " current=" . trim($file->curr
 --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
+After current+fgets: key=1 current=line 1