[mythtv] mythbackend 29/fixes crashes

[Ken Bass]

Another crash since a complete recompile with the latest 29/fixes.

What about this line would cause a crash and what needs to be fixed to 
protect against it? 80% of the crashes are on this line.

QString str = list->join("[]:[]");

#4  0x00007fdff34f29c4 in MythSocket::WriteStringListReal 
(this=0x1cc64f0, list=0x7fdef4ff7ad0, ret=0x7fdef4ff75af) at 
mythsocket.cpp:727
> 727     QString str = list->join("[]:[]");
>
> (gdb) p *list
> $3 = {<QList<QString>> = {<QListSpecialMethods<QString>> = {<No data 
> fields>}, {p = {static shared_null = {ref = {atomic = {
>               _q_value = {<std::__atomic_base<int>> = {_M_i = -1}, <No 
> data fields>}}}, alloc = 0, begin = 0, end = 0, array = {0x0}},
>         d = 0x7fdedc048f30}, d = 0x7fdedc048f30}}, <No data fields>}
>
> When it happens it is always the hour or 1/2 hour. I am not sure what 
> happens at time but I am pretty sure it happens while live TV is 
> playing somewhere. I don't think it I have seen it happen when idle or 
> just recording things.