Guaranteed activation of external link blocking

This is a quickfix for the problem observed with external link blocking
during certain history navigation actions (when the cached iframe content is
loaded/restored before the viewer setup is completed).

Since external link blocking doesn't depend on the translations (that
are asynchronously loaded during the viewer setup) it can be performed
unconditionally. However, the current dependence of `on_content_load()`
on viewer setup has to be addressed too.

static/skin/viewer.js

@@ -335,8 +335,8 @@ let viewerSetupComplete = false;
 function on_content_load() {
   if ( viewerSetupComplete ) {
     handle_content_url_change();
-    setup_external_link_blocker();
   }
+  setup_external_link_blocker();
 }
 
 function htmlDecode(input) {

test/server.cpp

@@ -73,7 +73,7 @@ const ResourceCollection resources200Compressible{
   { DYNAMIC_CONTENT, "/ROOT%23%3F/skin/taskbar.css" },
   { STATIC_CONTENT,  "/ROOT%23%3F/skin/taskbar.css?cacheid=bbdaf425" },
   { DYNAMIC_CONTENT, "/ROOT%23%3F/skin/viewer.js" },
-  { STATIC_CONTENT,  "/ROOT%23%3F/skin/viewer.js?cacheid=0c02871d" },
+  { STATIC_CONTENT,  "/ROOT%23%3F/skin/viewer.js?cacheid=cb9b1f75" },
   { DYNAMIC_CONTENT, "/ROOT%23%3F/skin/fonts/Poppins.ttf" },
   { STATIC_CONTENT,  "/ROOT%23%3F/skin/fonts/Poppins.ttf?cacheid=af705837" },
   { DYNAMIC_CONTENT, "/ROOT%23%3F/skin/fonts/Roboto.ttf" },
@@ -312,7 +312,7 @@ R"EXPECTEDRESULT(    <link type="text/css" href="./skin/taskbar.css?cacheid=bbda
     <link type="text/css" href="./skin/css/autoComplete.css?cacheid=08951e06" rel="Stylesheet" />
     <script type="module" src="./skin/i18n.js?cacheid=2cf0f8c5" defer></script>
     <script type="text/javascript" src="./skin/languages.js?cacheid=648526e1" defer></script>
-    <script type="text/javascript" src="./skin/viewer.js?cacheid=0c02871d" defer></script>
+    <script type="text/javascript" src="./skin/viewer.js?cacheid=cb9b1f75" defer></script>
     <script type="text/javascript" src="./skin/autoComplete.min.js?cacheid=1191aaaf"></script>
       const blankPageUrl = root + "/skin/blank.html?cacheid=6b1fa032";
             <img src="./skin/langSelector.svg?cacheid=00b59961">