Fixed a possible crash in dbase_open() on empty filename.

ext/dbase/dbase.c

@@ -129,6 +129,11 @@ PHP_FUNCTION(dbase_open)
 	convert_to_string_ex(dbf_name);
 	convert_to_long_ex(options);
 
+	if (!Z_STRLEN_PP(dbf_name)) {
+		php_error_docref(NULL TSRMLS_CC, E_WARNING, "The filename cannot be empty.");
+		RETURN_FALSE;
+	}
+
 	if (Z_LVAL_PP(options) == 1) {
 		php_error_docref(NULL TSRMLS_CC, E_WARNING, "Cannot open %s in write-only mode", Z_STRVAL_PP(dbf_name));
 		RETURN_FALSE;