Fix _pdo_pgsql_trim_message bad access

Author: dixyes

ext/pdo_pgsql/pgsql_driver.c

@@ -39,7 +39,13 @@ static bool pgsql_handle_in_transaction(pdo_dbh_t *dbh);
 
 static char * _pdo_pgsql_trim_message(const char *message, int persistent)
 {
-	size_t i = strlen(message)-1;
+    size_t i = strlen(message);
+    if (i == 0) {
+        char *ret = pemalloc(1, persistent);
+        ret[0] = '\0';
+        return ret;
+    }
+    i--;
 	char *tmp;
 
 	if (i>1 && (message[i-1] == '\r' || message[i-1] == '\n') && message[i] == '.') {