Show error message on widget when habit not found

Fixes #35

app/src/main/java/org/isoron/uhabits/widgets/BaseWidgetProvider.java

@@ -25,7 +25,6 @@ import android.appwidget.AppWidgetProvider;
 import android.content.Context;
 import android.content.SharedPreferences;
 import android.graphics.Bitmap;
-import android.media.Image;
 import android.os.Build;
 import android.os.Bundle;
 import android.preference.PreferenceManager;
@@ -33,7 +32,6 @@ import android.util.Log;
 import android.view.LayoutInflater;
 import android.view.View;
 import android.widget.ImageView;
-import android.widget.LinearLayout;
 import android.widget.RemoteViews;
 
 import org.isoron.helpers.DialogHelper;
@@ -106,6 +104,14 @@ public abstract class BaseWidgetProvider extends AppWidgetProvider
         if(habitId < 0) return;
 
         Habit habit = Habit.get(habitId);
+        if(habit == null)
+        {
+            RemoteViews errorView = new RemoteViews(context.getPackageName(),
+                    R.layout.widget_error);
+            manager.updateAppWidget(widgetId, errorView);
+            return;
+        }
+
         View widgetView = buildCustomView(context, habit);
         measureCustomView(context, width, height, widgetView);
 

app/src/main/res/layout/widget_error.xml

@@ -0,0 +1,41 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+  ~ Copyright (C) 2016 Álinson Santos Xavier <isoron@gmail.com>
+  ~
+  ~ This file is part of Loop Habit Tracker.
+  ~
+  ~ Loop Habit Tracker is free software: you can redistribute it and/or modify
+  ~ it under the terms of the GNU General Public License as published by the
+  ~ Free Software Foundation, either version 3 of the License, or (at your
+  ~ option) any later version.
+  ~
+  ~ Loop Habit Tracker is distributed in the hope that it will be useful, but
+  ~ WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+  ~ or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+  ~ more details.
+  ~
+  ~ You should have received a copy of the GNU General Public License along
+  ~ with this program. If not, see <http://www.gnu.org/licenses/>.
+  -->
+
+<LinearLayout
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent"
+    android:background="@drawable/widget_background"
+    android:gravity="center"
+    android:orientation="vertical"
+    android:paddingTop="4dp"
+    android:paddingBottom="0dp"
+    android:paddingLeft="8dp"
+    android:paddingRight="8dp">
+
+    <TextView
+        android:id="@+id/label"
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:gravity="center"
+        android:text="Habit not found"
+        android:textColor="#ffffff"/>
+
+</LinearLayout>