Add better error handling for API

lib/api.dart

@@ -182,15 +182,22 @@ class InvenTreeAPI {
     var response = await get("").timeout(Duration(seconds: 10)).catchError((error) {
 
       if (error is SocketException) {
-        errorMessage = "Could not connect to server.";
-        print(errorMessage);
-        throw errorMessage;
+        print("Could not connect to server");
+        return null;
+      } else if (error is TimeoutException) {
+        print("Server timeout");
+        return null;
       } else {
         // Unknown error type, re-throw error
+        print("Unknown error: ${error.toString()}");
         throw error;
       }
     });
 
+    if (response == null) {
+      return false;
+    }
+
     if (response.statusCode != 200) {
       print("Invalid status code: " + response.statusCode.toString());
       return false;

lib/main.dart

@@ -134,22 +134,6 @@ class _MyHomePageState extends State<MyHomePage> {
         onConnectFailure("Could not connect to server");
       }
 
-    }).catchError((e) {
-
-      String fault = "Connection error";
-
-      _serverConnection = false;
-      _serverStatusColor = Color.fromARGB(255, 250, 50, 50);
-
-      _serverStatus = "Error connecting to $_serverAddress";
-
-      if (e is TimeoutException) {
-        fault = "Timeout: No response from server";
-      } else {
-        fault = e.toString();
-      }
-
-      onConnectFailure(fault);
     });
 
     // Update widget state