do not save draft if message is completly empty and fixed appending shared text

src/main/java/eu/siacs/conversations/entities/Conversation.java

@@ -647,11 +647,12 @@ public class Conversation extends AbstractEntity implements Blockable, Comparabl
 		return null;
 	}
 
-	public boolean setNextMessage(String message) {
+	public boolean setNextMessage(final String input) {
+		final String message = input == null || input.trim().isEmpty() ? null : input;
 		boolean changed = !getNextMessage().equals(message);
 		this.setAttribute(ATTRIBUTE_NEXT_MESSAGE, message);
 		if (changed) {
-			this.setAttribute(ATTRIBUTE_NEXT_MESSAGE_TIMESTAMP, TextUtils.isEmpty(message) ? 0 : System.currentTimeMillis());
+			this.setAttribute(ATTRIBUTE_NEXT_MESSAGE_TIMESTAMP, message == null ? 0 : System.currentTimeMillis());
 		}
 		return changed;
 	}

src/main/java/eu/siacs/conversations/ui/ConversationFragment.java

@@ -2391,7 +2391,9 @@ public class ConversationFragment extends XmppFragment implements EditMessage.Ke
 			return;
 		}
 		String previous = this.binding.textinput.getText().toString();
-		if (previous.length() != 0 && !previous.endsWith(" ")) {
+		if (UIHelper.isLastLineQuote(previous)) {
+			text = '\n' + text;
+		} else if (previous.length() != 0 && !Character.isWhitespace(previous.charAt(previous.length() - 1))) {
 			text = " " + text;
 		}
 		this.binding.textinput.append(text);

src/main/java/eu/siacs/conversations/utils/UIHelper.java

@@ -334,6 +334,22 @@ public class UIHelper {
 		}
 	}
 
+	public static boolean isLastLineQuote(String body) {
+		if (body.endsWith("\n")) {
+			return false;
+		}
+		String[] lines = body.split("\n");
+		if (lines.length == 0) {
+			return false;
+		}
+		String line = lines[lines.length - 1];
+		if (line.isEmpty()) {
+			return false;
+		}
+		char first = line.charAt(0);
+		return first == '>' && isPositionFollowedByQuoteableCharacter(line,0) || first == '\u00bb';
+	}
+
 	public static CharSequence shorten(CharSequence input) {
 		return input.length() > 256 ? StylingHelper.subSequence(input, 0, 256) : input;
 	}