Issue #21951: Use attemptckalloc() instead of ckalloc() in Tkinter.

ckalloc() causes the Tcl interpreter to panic, attemptckalloc() returns NULL
if the memory allocation fails.
Issue #21951: Fixed a crash in Tkinter on AIX when called Tcl command with
empty string or tuple argument.

On some platforms Tcl memory allocator returns NULL when allocating zero-sized
block of memory.
Issue #21147: sqlite3 now raises an exception if the request contains a null
character instead of truncate it.  Based on patch by Victor Stinner.