Fix some crashes on old devices

app/src/main/java/org/isoron/uhabits/activities/BaseRootView.java

@@ -21,6 +21,7 @@ package org.isoron.uhabits.activities;
 
 import android.content.*;
 import android.support.annotation.*;
+import android.support.v4.content.res.*;
 import android.support.v7.widget.Toolbar;
 import android.view.*;
 import android.widget.*;
@@ -67,9 +68,8 @@ public abstract class BaseRootView extends FrameLayout
     {
         if (SDK_INT < LOLLIPOP && !themeSwitcher.isNightMode())
         {
-            return context
+            return ResourcesCompat.getColor(context.getResources(),
-                .getResources()
+                R.color.grey_900, context.getTheme());
-                .getColor(R.color.grey_900, context.getTheme());
         }
 
         StyledResources res = new StyledResources(context);

app/src/main/java/org/isoron/uhabits/activities/BaseScreen.java

@@ -26,6 +26,7 @@ import android.net.*;
 import android.os.*;
 import android.support.annotation.*;
 import android.support.design.widget.*;
+import android.support.v4.content.res.*;
 import android.support.v7.app.*;
 import android.support.v7.view.ActionMode;
 import android.support.v7.widget.Toolbar;
@@ -103,9 +104,8 @@ public class BaseScreen
     {
         if (SDK_INT < LOLLIPOP)
         {
-            return context
+            return ResourcesCompat.getColor(context.getResources(),
-                .getResources()
+                R.color.grey_900, context.getTheme());
-                .getColor(R.color.grey_900, context.getTheme());
         }
         else
         {

app/src/main/java/org/isoron/uhabits/activities/common/dialogs/HistoryEditorDialog.java

@@ -163,6 +163,9 @@ public class HistoryEditorDialog extends AppCompatDialogFragment
         @Override
         public void onPostExecute()
         {
+            if (getContext() == null || habit == null || historyChart == null)
+                return;
+
             int color = ColorUtils.getColor(getContext(), habit.getColor());
             historyChart.setColor(color);
             historyChart.setCheckmarks(checkmarks);

app/src/main/java/org/isoron/uhabits/activities/habits/list/views/HabitCardView.java

@@ -239,7 +239,7 @@ public class HabitCardView extends FrameLayout
                 background = res.getDrawable(R.attr.selectedBackground);
             else background = res.getDrawable(R.attr.cardBackground);
 
-            innerFrame.setBackground(background);
+            innerFrame.setBackgroundDrawable(background);
         }
     }
 

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

@@ -144,12 +144,18 @@ public abstract class BaseWidget
         return new int[]{ w, h, w, h };
     }
 
+    @NonNull
     private Bitmap getBitmapFromView(View view)
     {
         view.invalidate();
         view.setDrawingCacheEnabled(true);
         view.buildDrawingCache(true);
-        return view.getDrawingCache();
+        Bitmap drawingCache = view.getDrawingCache();
+
+        if(drawingCache == null)
+            throw new IllegalStateException("bitmap is null");
+
+        return drawingCache;
     }
 
     @NonNull