Added check to prevent page down from looping endlessly

editor.c

@@ -124,7 +124,7 @@ void page_down_handler(Buffer* buffer) {
 				once, so this hardcoded statement is fine. */
 
 
-	while (*(buffer->start - 1) != '\n') {
+	while ((*(buffer->start - 1) != '\n') && (buffer->end != (buffer->text + buffer->size))) {
 		buffer_right(buffer);
 	}