[2.7] bpo-34794: Fix a memory leak in Tkinter.Image.

[serhiy-storchaka]

A Tcl object was leaked when set the data or maskdata options.

https://bugs.python.org/issue34794

[zhangyangyu]

According to https://www.tcl.tk/man/tcl/TclLib/ByteArrObj.html, the result of Tcl_NewByteArrayObj is of zero reference count. It looks to me the problem seems to exist in AsObj. AsObj returns a tcl object with zero reference count in other cases, but when the arg is a PyTclObject, it increases another reference count which seems redundant to me. I am not familiar with the code and correct me if I am wrong.

[serhiy-storchaka]

Thank you @zhangyangyu. Your analysis is absolutely correct. Opened #10025 for the new fix.