FIX: email excerpts for posts starting with a quote were displaying a username

If a post starts with a post quote and has no other text content,
then the email excerpt was the name of the person quoted and
nothing else. The intention was to show the contents of the
first paragraph or div after the quote.

With this change, a quote followed by an image will use the
image as the excerpt. A quote followed by a onebox will use the
onebox.

app/helpers/user_notifications_helper.rb

@@ -47,8 +47,9 @@ module UserNotificationsHelper
 
     return result unless result.blank?
 
-    # If there is no first paragaph, return the first div (onebox)
-    doc.css('div').first
+    # If there is no first paragaph with text, return the first paragraph with
+    # something else (an image) or div (a onebox).
+    doc.css('body > p, body > div').first
   end
 
   def email_excerpt(html_arg, post = nil)

spec/helpers/user_notifications_helper_spec.rb

@@ -13,6 +13,19 @@ describe UserNotificationsHelper do
       paragraphs.join("\n")
     end
 
+    let(:post_quote) do
+      <<~HTML
+        <aside class="quote no-group" data-post="859" data-topic="30">
+        <div class="title">
+        <div class="quote-controls"></div>
+        <img alt width="20" height="20" src="https://example.com/m.png" class="avatar"> modman:</div>
+        <blockquote>
+        <p>This is a post quote</p>
+        </blockquote>
+        </aside>
+      HTML
+    end
+
     it "can return the first paragraph" do
       SiteSetting.digest_min_excerpt_length = 50
       expect(helper.email_excerpt(cooked)).to eq(paragraphs[0])
@@ -54,6 +67,24 @@ describe UserNotificationsHelper do
 
       expect(helper.email_excerpt(cooked)).to eq "<p>BEFORE</p><blockquote>\n  <p>This is a user quote</p>\n</blockquote><p>AFTER</p>"
     end
+
+    it "defaults to content after post quote (image w/ no text)" do
+      image_paragraph = '<p><img src="//localhost:3000/uploads/b9.png" width="300" height="300"></p>'
+      cooked = <<~HTML
+        #{post_quote}
+        #{image_paragraph}
+      HTML
+      expect(helper.email_excerpt(cooked)).to eq(image_paragraph)
+    end
+
+    it "defaults to content after post quote (onebox)" do
+      aside_onebox = '<aside class="onebox wikipedia"><article class="onebox-body"><p>Onebox excerpt here</p></article><div class="onebox-metadata"></div></aside>'
+      cooked = <<~HTML
+        #{post_quote}
+        #{aside_onebox}
+      HTML
+      expect(helper.email_excerpt(cooked)).to eq(aside_onebox)
+    end
   end
 
   describe '#logo_url' do