MV3: refactor opening viewer via extension action

Catching the Promise rejection in executeScript handles all the special
pages better, than listing the individual protocols. This automatically
covers the webstores, hence fixes the action not working when clicked
immediately after installing, while still on the webstore page.

src/scripts/mv3/service-worker.js

@@ -9,7 +9,6 @@ chrome.action.onClicked.addListener(newViewer);
 chrome.runtime.onMessage.addListener(respond);
 
 const baseUrl = chrome.runtime.getURL("pdfjs/web/viewer.html");
-const extProto = new URL(baseUrl).protocol;
 const messageUrl = getViewerURL("/pages/Access Denied");
 const splashUrl = getViewerURL("/pages/Open File");
 const autoOpener = "scripts/mv3/content-script.js";
@@ -118,37 +117,27 @@ function resetMenus(permit) {
 /* Open current URL in a new viewer tab, if it is a PDF;
  * otherwise open a blank viewer with the splash screen */
 async function newViewer(tab) {
+  const hasFilesAccess = () => {
+    /* Work around Chromium bug: activeTab insufficient for file: URL access */
+    chrome.permissions.request({ origins: [url] }).catch(r => {});
+    return chrome.extension.isAllowedFileSchemeAccess();
+  };
   const url = tab.url;
   let viewerUrl = splashUrl;
-  switch (new URL(url).protocol) {
-    case "chrome:":
-    case "edge:":
-    case "opera:":
-    case "brave:":
-    case "about:":
-    case extProto:
-      break;
-    case "file:":
-      /* Work around Chromium bug: activeTab insufficient for file: URL access */
-      chrome.permissions.request({ origins: [url] }).catch(r => {});
-      if (!await chrome.extension.isAllowedFileSchemeAccess()) {
-        viewerUrl = messageUrl;
-        break;
-      }
-      /* else fall through */
-    default:
-      if (await isPdfTab(tab))
-        viewerUrl = getViewerURL(url);
+  if (new URL(url).protocol === "file:" && !await hasFilesAccess()) {
+    viewerUrl = messageUrl;
+  } else if (await isPdfContent(tab)) {
+    viewerUrl = getViewerURL(url);
   }
   chrome.tabs.create({ url: viewerUrl, index: tab.index + 1 });
 }
 
 /* Check if the document MIME type is PDF in given tab */
-async function isPdfTab(tab) {
+async function isPdfContent(tab) {
   const results = await chrome.scripting.executeScript({
     target: { tabId: tab.id },
     func: () => document.contentType
-  });
+  }).catch(r => {});
   if (results) {
     const {frameId, result} = results[0];
     if (frameId === 0 && result?.includes("application/pdf"))