Network.erl fix sta_rssi() crash when not started.

Calling network:sta_rssi() would crash if network was not started.

Handle this and return error tuple, and added test.

Signed-off-by: Peter M <petermm@gmail.com>

libs/eavmlib/src/network.erl

@@ -295,13 +295,17 @@ stop() ->
 %%-----------------------------------------------------------------------------
 -spec sta_rssi() -> {ok, Rssi :: db()} | {error, Reason :: term()}.
 sta_rssi() ->
-    Port = get_port(),
-    Ref = make_ref(),
-    Port ! {self(), Ref, rssi},
-    receive
-        {Ref, {error, Reason}} -> {error, Reason};
-        {Ref, {rssi, Rssi}} -> {ok, Rssi};
-        Other -> {error, Other}
+    case whereis(network_port) of
+        undefined ->
+            {error, network_down};
+        Pid ->
+            Ref = make_ref(),
+            Pid ! {self(), Ref, rssi},
+            receive
+                {Ref, {error, Reason}} -> {error, Reason};
+                {Ref, {rssi, Rssi}} -> {ok, Rssi};
+                Other -> {error, Other}
+            end
     end.
 
 %%

src/platforms/esp32/test/main/test_erl_sources/test_wifi_example.erl

@@ -25,6 +25,7 @@
 start() ->
     case verify_platform(atomvm:platform()) of
         ok ->
+            network:sta_rssi(),
             ok = start_network(),
             ok = network:stop(),
             start_network(),
@@ -59,7 +60,8 @@ start_network() ->
     ],
     case network:start(Config) of
         {ok, _Pid} ->
-            io:format("Network started.~n");
+            io:format("Network started.~n"),
+            ok;
         Error ->
             Error
     end.