fix: only display "Viewed" checkbox if fileContentToggle is set

Author: Pierrci

src/ui/css/diff2html.css

@@ -74,7 +74,7 @@
 
 .d2h-file-collapse {
   justify-content: flex-end;
-  display: flex;
+  display: none;
   cursor: pointer;
   font-size: 12px;
   align-items: center;

src/ui/js/diff2html-ui-base.ts

@@ -112,7 +112,9 @@ export class Diff2HtmlUI {
   }
 
   fileContentToggle(): void {
-    this.targetElement.querySelectorAll('.d2h-file-collapse').forEach(fileContentToggleBtn => {
+    this.targetElement.querySelectorAll<HTMLElement>('.d2h-file-collapse').forEach(fileContentToggleBtn => {
+      fileContentToggleBtn.style.display = 'flex';
+
       const toggleFileContents: (selector: string) => void = selector => {
         const fileContents: HTMLElement | null | undefined = fileContentToggleBtn
           .closest('.d2h-file-wrapper')