Fix crash when opening URL:s in Android < 7.0

In versions of Android earlier than 7.0 the FLAG_ACTIVITY_NEW_TASK
is needed when starting an activity from a non-activity context.

This was removed in Android 7.0 (possibly by mistake), see
https://code.google.com/p/android/issues/detail?id=226647.

Fixes #802

app/src/main/java/com/termux/app/TermuxOpenReceiver.java

@@ -31,6 +31,7 @@ public class TermuxOpenReceiver extends BroadcastReceiver {
         final boolean isExternalUrl = data.getScheme() != null && !data.getScheme().equals("file");
         if (isExternalUrl) {
             Intent viewIntent = new Intent(Intent.ACTION_VIEW, data);
+            viewIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
             try {
                 context.startActivity(viewIntent);
             } catch (ActivityNotFoundException e) {