Segfault when string2state() in iwd.c is passed a null pointer

With the latest IWD 0.9, connman somehow ends up getting a null pointer. The crash is in string2state() in iwd.c

I was able to fix this issue by patching connman so it doesn't try and use strcmp() on a null string. The patch is attached. I have also attached a gdb backtrace.

I have checked and it doesn't segfault in IWD 0.7, and may or may not segfault with IWD 0.8. While IWD may or may not be doing something wrong here, I believe this still needs to be fixed in connman, and possibly show a warning in the connman output if desired (as my patch does).

With the patch applied, connman works normally, and I only get a single warning that string2state() was passed a null string toward the very beginning of connmand starting (it doesn't seem to ever happen at any other time).

Edit: Looking into it, you use g_strcmp0 in other places in iwd.c and the documentation states it handles NULL strings gracefully. So it would likely be advantageous to change all uses of strcmp to g_strcmp0 to avoid other potential segfaults.