Skip conversion from detected ASCII

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

@@ -2064,8 +2064,15 @@ public class MessageHelper {
                                     if (c.equals(detected))
                                         break;
 
+                                    // Common detected/meta
+                                    // - windows-1250, windows-1257 / ISO-8859-1
+                                    // - ISO-8859-1 / windows-1252
+                                    // - US-ASCII / windows-1250, windows-1252, ISO-8859-1, ISO-8859-15, UTF-8
+
                                     if (StandardCharsets.US_ASCII.equals(detected) &&
-                                            ("windows-1252".equals(c.name()) ||
+                                            ("ISO-8859-15".equals(c.name()) ||
+                                                    "windows-1250".equals(c.name()) ||
+                                                    "windows-1252".equals(c.name()) ||
                                                     StandardCharsets.UTF_8.equals(c) ||
                                                     StandardCharsets.ISO_8859_1.equals(c)))
                                         break;