sim: fix segfault in sim atom

While adding the sim pin cache feature, pin_name could cause issue in
cases when sim pin is not there.

log:
ofonod[27810]: drivers/atmodem/sim.c:at_cpin_cb() crsm_pin_cb: READY
ofonod[27810]: src/sim.c:sim_pin_query_cb() sim->pin_type: 0, pin_type: 0
ofonod[27810]: Aborting (signal 11) [./src/ofonod]
ofonod[27810]: ++++++++ backtrace ++++++++
ofonod[27810]: #0  0x7fb7a7586cb0 in /lib/x86_64-linux-gnu/libc.so.6
ofonod[27810]: #1  0x7fb7a7693cd8 in /lib/x86_64-linux-gnu/libc.so.6
ofonod[27810]: sailfish-on-dontbeevil#2  0x4d899b in sim_pin_query_cb() at src/sim.c:3174
ofonod[27810]: sailfish-on-dontbeevil#3  0x4649e7 in at_cpin_cb() at drivers/atmodem/sim.c:1304
ofonod[27810]: sailfish-on-dontbeevil#4  0x4a5d70 in at_chat_finish_command() at gatchat/gatchat.c:462

ofono/src/sim.c

@@ -3300,7 +3300,7 @@ static void sim_pin_query_cb(const struct ofono_error *error,
 	DBusConnection *conn = ofono_dbus_get_connection();
 	const char *path = __ofono_atom_get_path(sim->atom);
 	struct cached_pin *cpins = pin_cache_lookup(sim->iccid);
-	const char *pin_name;
+	const char *pin_name = sim_passwd_name(pin_type);
 	char **locked_pins;
 	gboolean lock_changed;
 
@@ -3313,7 +3313,6 @@ static void sim_pin_query_cb(const struct ofono_error *error,
 
 	if (sim->pin_type != pin_type) {
 		sim->pin_type = pin_type;
-		pin_name = sim_passwd_name(pin_type);
 
 		if (pin_type != OFONO_SIM_PASSWORD_NONE &&
 				password_is_pin(pin_type) == FALSE)