Consider operations with file not found as unrecoverable

app/src/main/java/eu/faircode/email/Core.java

@@ -57,6 +57,7 @@ import org.jsoup.nodes.Element;
 import java.io.BufferedInputStream;
 import java.io.File;
 import java.io.FileInputStream;
+import java.io.FileNotFoundException;
 import java.io.FileOutputStream;
 import java.io.IOException;
 import java.io.InputStream;
@@ -263,6 +264,7 @@ class Core {
 
                         if (ex instanceof OutOfMemoryError ||
                                 ex instanceof MessageRemovedException ||
+                                ex instanceof FileNotFoundException ||
                                 ex instanceof FolderNotFoundException ||
                                 ex instanceof IllegalArgumentException ||
                                 ex.getCause() instanceof CommandFailedException) {

app/src/main/java/eu/faircode/email/ServiceSend.java

@@ -36,6 +36,7 @@ import androidx.core.content.ContextCompat;
 import androidx.lifecycle.Observer;
 import androidx.preference.PreferenceManager;
 
+import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.net.Inet4Address;
 import java.net.Inet6Address;
@@ -166,6 +167,7 @@ public class ServiceSend extends ServiceBase {
 
                                             if (ex instanceof OutOfMemoryError ||
                                                     ex instanceof MessageRemovedException ||
+                                                    ex instanceof FileNotFoundException ||
                                                     ex instanceof SendFailedException ||
                                                     ex instanceof IllegalArgumentException) {
                                                 Log.w("Unrecoverable");