Added DelSp support

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

@@ -1891,7 +1891,7 @@ public class HtmlHelper {
     }
 
     // https://tools.ietf.org/html/rfc3676
-    static String flow(String text) {
+    static String flow(String text, boolean delsp) {
         boolean continuation = false;
         StringBuilder flowed = new StringBuilder();
         String[] lines = text.split("\\r?\\n");
@@ -1899,6 +1899,9 @@ public class HtmlHelper {
             String line = lines[l];
             lines[l] = null;
 
+            if (delsp && line.length() > 0)
+                line = line.substring(0, line.length() - 1);
+
             if (continuation)
                 while (line.startsWith(">")) {
                     line = line.substring(1);

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

@@ -2917,8 +2917,10 @@ public class MessageHelper {
                     } else if (StandardCharsets.UTF_8.equals(cs))
                         result = CharsetHelper.utf8toW1252(result);
 
+                    // https://datatracker.ietf.org/doc/html/rfc3676
                     if ("flowed".equalsIgnoreCase(h.contentType.getParameter("format")))
-                        result = HtmlHelper.flow(result);
+                        result = HtmlHelper.flow(result,
+                                "yes".equalsIgnoreCase(h.contentType.getParameter("delsp")));
 
                     // https://www.w3.org/QA/2002/04/valid-dtd-list.html
                     if (result.length() > DOCTYPE.length()) {