[FIX] website: set the correct height for welcome message

Commit 48a1eaf7 adapt the welcome
message on website so that it fits the page height. But this does
only worked for large screens as the height was forced to main
height... which is smaller than the default welcome message height
on small screen. The fix only had to use min-height instead of height.

addons/website/static/src/js/website.editor.js

@@ -216,7 +216,7 @@ base.ready().then(function () {
         var $wrap = $("#wrapwrap.homepage #wrap");
         if ($wrap.length && $wrap.html().trim() === "") {
             var $welcome_message = $(qweb.render("website.homepage_editor_welcome_message"));
-            $welcome_message.css("height", $wrap.parent("main").height() - ($wrap.outerHeight(true) - $wrap.height()));
+            $welcome_message.css("min-height", $wrap.parent("main").height() - ($wrap.outerHeight(true) - $wrap.height()));
             $wrap.empty().append($welcome_message);
         }
     }