Added no body warning

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

@@ -538,8 +538,10 @@ public class MessageHelper {
         private List<String> warnings = new ArrayList<>();
 
         String getHtml(Context context) throws MessagingException {
-            if (plain == null && html == null)
+            if (plain == null && html == null) {
+                warnings.add(context.getString(R.string.title_no_body));
                 return null;
+            }
 
             String result;
             boolean text = false;

app/src/main/res/values/strings.xml

@@ -439,6 +439,7 @@
     <string name="title_report">Report</string>
     <string name="title_no_ask_again">Do not ask this again</string>
     <string name="title_no_adobe">Adobe Acrobat reader cannot open safely shared files, see the FAQ for more information</string>
+    <string name="title_no_body">No message text found</string>
     <string name="title_no_charset">Unsupported encoding: %1$s</string>
 
     <string name="title_try">Try FairEmail, an open source, privacy friendly email app for Android</string>