Fix multi-line quotes being cut off

This was a mistake in the code that was designed to remove the outside
paragraphs, which seems to be to make way for the quotation marks we
add around the text. Instead of doing that (which turns out, is very
brittle and breaks on multiple paragraphs) insert the quotation marks
*inside* of the paragraph tags.

A test case is added for this as well.

autotests/texthandlertest.cpp

@@ -530,6 +530,9 @@ void TextHandlerTest::componentOutput_data()
     QTest::newRow("quote") << u"<p>Text</p>\n<blockquote>\n<p>blockquote</p>\n</blockquote>"_s
                            << QList<MessageComponent>{MessageComponent{MessageComponentType::Text, u"Text"_s, {}},
                                                       MessageComponent{MessageComponentType::Quote, u"“blockquote”"_s, {}}};
+    QTest::newRow("multiple paragraph quote") << u"<blockquote>\n<p>blockquote</p>\n<p>next paragraph</p>\n</blockquote>"_s
+                                              << QList<MessageComponent>{
+                                                     MessageComponent{MessageComponentType::Quote, u"<p>“blockquote</p>\n<p>next paragraph”</p>"_s, {}}};
     QTest::newRow("no tag first paragraph") << u"Text\n<p>Text</p>"_s
                                             << QList<MessageComponent>{MessageComponent{MessageComponentType::Text, u"Text"_s, {}},
                                                                        MessageComponent{MessageComponentType::Text, u"Text"_s, {}}};