FIX: Correctly display GitHub code oneboxes (#14149)

FIX: Correctly display GitHub code oneboxes (#14149)

Code fragments without the code lines were not displayed correctly.

Follow-up-to 721a946d77b2c07170273bcbc5b9dcc968829d6d.

diff --git a/lib/email/styles.rb b/lib/email/styles.rb
index 1f3edce..416798e 100644
--- a/lib/email/styles.rb
+++ b/lib/email/styles.rb
@@ -212,7 +212,8 @@ module Email
       style('span.post-count', 'margin: 0 5px; color: #777;')
       style('pre', 'word-wrap: break-word; max-width: 694px;')
       style('code', 'background-color: #f9f9f9; padding: 2px 5px;')
-      style('pre code', 'display: block; background-color: #f9f9f9; overflow: auto; padding: 5px; white-space: normal;')
+      style('pre code', 'display: block; background-color: #f9f9f9; overflow: auto; padding: 5px;')
+      style('pre.onebox code', 'white-space: normal;')
       style('pre code li', 'white-space: pre;')
       style('.featured-topic a', "text-decoration: none; font-weight: bold; color: #{SiteSetting.email_link_color}; line-height:1.5em;")
       style('.summary-email', "-moz-box-sizing:border-box;-ms-text-size-adjust:100%;-webkit-box-sizing:border-box;-webkit-text-size-adjust:100%;box-sizing:border-box;color:#0a0a0a;font-family:Arial,sans-serif;font-size:14px;font-weight:400;line-height:1.3;margin:0;min-width:100%;padding:0;width:100%")

GitHub sha: f0005025c4cce53fe9c6cdbe932831f63d5d3ae5

This commit appears in #14149 which was approved by eviltrout. It was merged by nbianca.