Fix MySQL memory leak

Before commit 1f987e7, there were issues upgrading my music database to
the latest format (because of duplicate keys, which are solved by using
REPLACE instead of INSERT).

This pointed out a severe memory leak in
xbmc/dbwrappers/mysqldataset.cpp, which is confirmed by valgrind.

This is an attempt to fix the leak, and should solve xbmc#12459.

xbmc/dbwrappers/mysqldataset.cpp

@@ -240,7 +240,10 @@ int MysqlDatabase::copy(const char *backup_name) {
     // create the new database
     sprintf(sql, "CREATE DATABASE `%s`", backup_name);
     if ( (ret=query_with_reconnect(sql)) != MYSQL_OK )
+    {
+      mysql_free_result(res);
       throw DbErrors("Can't create database for copy: '%s' (%d)", db.c_str(), ret);
+    }
 
     MYSQL_ROW row;
 
@@ -252,15 +255,22 @@ int MysqlDatabase::copy(const char *backup_name) {
               backup_name, row[0], row[0]);
 
       if ( (ret=query_with_reconnect(sql)) != MYSQL_OK )
+      {
+        mysql_free_result(res);
         throw DbErrors("Can't copy schema for table '%s'\nError: %s", db.c_str(), ret);
+      }
 
       // copy the table data
       sprintf(sql, "INSERT INTO %s.%s SELECT * FROM %s",
               backup_name, row[0], row[0]);
 
       if ( (ret=query_with_reconnect(sql)) != MYSQL_OK )
+      {
+        mysql_free_result(res);
         throw DbErrors("Can't copy data for table '%s'\nError: %s", row[0], ret);
+      }
     }
+    mysql_free_result(res);
 
     // after table are recreated and repopulated we can recreate views
     // grab a list of views and their definitions
@@ -279,7 +289,10 @@ int MysqlDatabase::copy(const char *backup_name) {
                 backup_name, row[0], row[1]);
 
         if ( (ret=query_with_reconnect(sql)) != MYSQL_OK )
+        {
+          mysql_free_result(resViews);
           throw DbErrors("Can't create view '%s'\nError: %s", db.c_str(), ret);
+        }
       }
       mysql_free_result(resViews);
     }
@@ -336,6 +349,7 @@ long MysqlDatabase::nextid(const char* sname) {
     lengths = mysql_fetch_lengths(res);
     CLog::Log(LOGINFO,"Next id is [%.*s] ", (int) lengths[0], row[0]);
     sprintf(sqlcmd,"update %s set nextid=%d where seq_name = '%s'",seq_table,id,sname);
+    mysql_free_result(res);
     if ((last_err = query_with_reconnect(sqlcmd) != 0)) return DB_UNEXPECTED_RESULT;
     return id;
   }