Fixed html charset edge case

app/src/main/java/com/sun/mail/handlers/text_plain.java

@@ -146,10 +146,7 @@ public class text_plain extends handler_base {
 	    String charset = ct.getParameter("charset");
 	    if (charset == null)
 		// If the charset parameter is absent, use US-ASCII.
-		charset = "us-ascii";
+		charset = StandardCharsets.ISO_8859_1.name();
-		if ("us-ascii".equals(charset) &&
-				"text/html".equalsIgnoreCase(ct.getBaseType()))
-			charset = StandardCharsets.UTF_8.name();
 	    return MimeUtility.javaCharset(charset);
 	} catch (Exception ex) {
 	    return null;

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

@@ -1907,8 +1907,11 @@ public class MessageHelper {
                         result = HtmlHelper.flow(result);
                     result = "<div x-plain=\"true\">" + HtmlHelper.formatPre(result) + "</div>";
                 } else if (h.isHtml()) {
-                    // Fix incorrect UTF16
+                    if (charset == null) {
-                    if (charset != null)
+                        if (CharsetHelper.isUTF8(result))
+                            result = new String(result.getBytes(StandardCharsets.ISO_8859_1), StandardCharsets.UTF_8);
+                    } else {
+                        // Fix incorrect UTF16
                         try {
                             Charset c = Charset.forName(charset);
                             if (CHARSET16.contains(c)) {
@@ -1924,6 +1927,7 @@ public class MessageHelper {
                         } catch (Throwable ex) {
                             Log.w(ex);
                         }
+                    }
 
                     if (charset == null) {
                         // <meta charset="utf-8" />