Fix the following nasty bug:

- if compile bails out from the middle of compiling, current_buffer is not restored
- if current_buffer is not null, yy_switch_to_buffer will do: *yy_c_buf_p = yy_hold_char; on
the next request
- which would lead to memory corruption on next request

Zend/zend_language_scanner.l

@@ -129,6 +129,7 @@ void startup_scanner(TSRMLS_D)
 	RESET_DOC_COMMENT();
 	SCNG(yy_start_stack_ptr) = 0;
 	SCNG(yy_start_stack_depth) = 0;
+	SCNG(current_buffer) = NULL;
 #ifdef ZEND_MULTIBYTE
 	SCNG(script_org) = NULL;
 	SCNG(script_org_size) = 0;