fixed memory leak in func (stmt *Statement) ParseWithSpecialTableName

[ManyakRus]

• Do only one thing
• Non breaking API changes
• Tested

What did this pull request do?

*fixed memory leak in func (stmt Statement) ParseWithSpecialTableName

need fill nil value after using, for prevent memory leak
tables = nil

User Case Description

Gorm function WithContext() have big memory leak.
In golang version 1.2.21 my request solve all problems with memory leak.
in golang version higher gorm have another new one memory leak.

[last-warrior]

how is this fixing memory leak ? You have commented out tables=nil . Now it's just expanded if condition.

[ManyakRus]

my fix not fix memeory leak i think :-(
i am sorry
it worked at first, but not now.

however Gorm function WithContext() have big memory leak.
I deleted WithContext() everywhere and problem fixed for me, but it is not good solve

[jinzhu]

WithContext doesn't leak memory, maybe the ctx you created leaks