catch and show exceptions thrown at importing events from a file

app/src/main/kotlin/com/simplemobiletools/calendar/pro/activities/MainActivity.kt

@@ -866,10 +866,14 @@ class MainActivity : SimpleActivity(), RefreshRecyclerViewListener {
                     return
                 }
 
+                try {
                     val inputStream = contentResolver.openInputStream(uri)
                     val out = FileOutputStream(tempFile)
                     inputStream!!.copyTo(out)
                     showImportEventsDialog(tempFile.absolutePath)
+                } catch (e: Exception) {
+                    showErrorToast(e)
+                }
             }
             else -> toast(R.string.invalid_file_format)
         }