fix some crashes related to saving files

app/src/main/kotlin/com/simplemobiletools/draw/activities/MainActivity.kt

@@ -326,8 +326,12 @@ class MainActivity : SimpleActivity(), CanvasListener {
     private fun saveImageFile(path: String) {
         val fileDirItem = FileDirItem(path, path.getFilenameFromPath())
         getFileOutputStream(fileDirItem, true) {
-            writeToOutputStream(path, it!!)
+            if (it != null) {
+                writeToOutputStream(path, it)
                 toast(R.string.file_saved)
+            } else {
+                toast(R.string.unknown_error_occurred)
+            }
         }
     }
 

app/src/main/kotlin/com/simplemobiletools/draw/models/Svg.kt

@@ -21,10 +21,14 @@ object Svg {
         val backgroundColor = (canvas.background as ColorDrawable).color
 
         activity.getFileOutputStream(FileDirItem(path, path.getFilenameFromPath()), true) {
+            if (it != null) {
                 val writer = BufferedWriter(OutputStreamWriter(it))
                 writeSvg(writer, backgroundColor, canvas.mPaths, canvas.width, canvas.height)
                 writer.close()
                 activity.toast(R.string.file_saved)
+            } else {
+                activity.toast(R.string.unknown_error_occurred)
+            }
         }
     }