Conditionally upgrade HTML to UTF8

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

@@ -1876,7 +1876,6 @@ public class MessageHelper {
                 if ((TextUtils.isEmpty(charset) || charset.equalsIgnoreCase(StandardCharsets.US_ASCII.name())))
                     charset = null;
 
-                if (h.isPlainText()) {
                 Charset cs = null;
                 try {
                     if (charset != null)
@@ -1884,6 +1883,7 @@ public class MessageHelper {
                 } catch (UnsupportedCharsetException ignored) {
                 }
 
+                if (h.isPlainText()) {
                     if (charset == null || StandardCharsets.ISO_8859_1.equals(cs)) {
                         Charset detected = CharsetHelper.detect(result);
                         if (StandardCharsets.ISO_8859_1.equals(cs) &&
@@ -1907,27 +1907,28 @@ public class MessageHelper {
                         result = HtmlHelper.flow(result);
                     result = "<div x-plain=\"true\">" + HtmlHelper.formatPre(result) + "</div>";
                 } else if (h.isHtml()) {
-                    if (charset == null) {
+                    // Conditionally upgrade to UTF8
-                        if (CharsetHelper.isUTF8(result))
+                    if ((cs == null ||
+                            StandardCharsets.US_ASCII.equals(cs) ||
+                            StandardCharsets.ISO_8859_1.equals(cs)) &&
+                            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(cs)) {
-                            if (CHARSET16.contains(c)) {
                             Charset detected = CharsetHelper.detect(result);
                             if (!CHARSET16.contains(detected))
-                                    Log.e(new Throwable("Charset=" + c + " detected=" + detected));
+                                Log.e(new Throwable("Charset=" + cs + " detected=" + detected));
                             if (StandardCharsets.US_ASCII.equals(detected) ||
                                     StandardCharsets.UTF_8.equals(detected)) {
                                 charset = null;
-                                    result = new String(result.getBytes(c), detected);
+                                result = new String(result.getBytes(cs), detected);
                             }
                         }
                     } catch (Throwable ex) {
                         Log.w(ex);
                     }
-                    }
 
                     if (charset == null) {
                         // <meta charset="utf-8" />