Minor validations in order to avoid warnings

main/install/install.lib.php

@@ -611,9 +611,13 @@ function database_server_connect() {
  * @return boolean 
  */
 function database_exists($database_name) {    
+    if (empty($database_name)) {
+        return false;
+    }    
     $select_database = @Database::select_db($database_name);    
     $show_database = false;    
-    $result = @Database::query("SHOW DATABASES LIKE '".Database::escape_string($database_name)."' ");
+    $sql = "SHOW DATABASES LIKE '".addslashes($database_name)."'";    
+    $result = @Database::query($sql);
     if (Database::num_rows($result)) {
         $show_database = true;
     }