Allow/fix review (approve/reject) of empty PRs (#25690)

gitea allows to create empty PRs.

Currently when you need approvals for a merge, you have to manually add
/files to the url to get to the files tab to approve / reject the PR.

This PR allows to open the files tab via the normal tab / link and then
fixes the layout of the files tab.

**Screenshots:**

Before:

![image](https://github.com/go-gitea/gitea/assets/1135157/b5082e5e-8c32-4412-993e-b854905e96d3)

After:

![image](https://github.com/go-gitea/gitea/assets/1135157/1f5e056e-396f-4dfb-8d14-e17a2f6495d9)

---------

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: Giteabot <teabot@gitea.io>

templates/repo/diff/box.tmpl

@@ -1,20 +1,7 @@
-{{if .DiffNotAvailable}}
-	<div>
-		<div class="diff-detail-box diff-box sticky">
-			<div class="ui right">
-				{{template "repo/diff/whitespace_dropdown" .}}
-				{{template "repo/diff/options_dropdown" .}}
-				{{if and .PageIsPullFiles $.SignedUserID (not .IsArchived)}}
-					{{template "repo/diff/new_review" .}}
-				{{end}}
-			</div>
-		</div>
-	</div>
-	<h4>{{.locale.Tr "repo.diff.data_not_available"}}</h4>
-{{else}}
-	<div>
+<div>
 	<div class="diff-detail-box diff-box sticky gt-df gt-sb gt-ac gt-fw">
 		<div class="gt-df gt-ac gt-fw">
+			{{if not .DiffNotAvailable}}
 				<button class="diff-toggle-file-tree-button gt-df gt-ac not-mobile" data-show-text="{{.locale.Tr "repo.diff.show_file_tree"}}" data-hide-text="{{.locale.Tr "repo.diff.hide_file_tree"}}">
 					{{/* the icon meaning is reversed here, "octicon-sidebar-collapse" means show the file tree */}}
 					{{svg "octicon-sidebar-collapse" 20 "icon gt-hidden"}}
@@ -31,9 +18,10 @@
 				<div class="diff-detail-stats gt-df gt-ac gt-fw">
 					{{svg "octicon-diff" 16 "gt-mr-2"}}{{.locale.Tr "repo.diff.stats_desc" .Diff.NumFiles .Diff.TotalAddition .Diff.TotalDeletion | Str2html}}
 				</div>
+			{{end}}
 		</div>
 		<div class="diff-detail-actions gt-df gt-ac gt-gap-2 gt-fw">
-				{{if and .PageIsPullFiles $.SignedUserID (not .IsArchived)}}
+			{{if and .PageIsPullFiles $.SignedUserID (not .IsArchived) (not .DiffNotAvailable)}}
 				<div class="gt-df gt-ac gt-fc gt-whitespace-nowrap gt-mr-2">
 					<label for="viewed-files-summary" id="viewed-files-summary-label" data-text-changed-template="{{.locale.Tr "repo.pulls.viewed_files_label"}}">
 						{{.locale.Tr "repo.pulls.viewed_files_label" .Diff.NumViewedFiles .Diff.NumFiles}}
@@ -48,6 +36,7 @@
 			{{end}}
 		</div>
 	</div>
+	{{if not .DiffNotAvailable}}
 		<script id="diff-data-script" type="module">
 			const diffDataFiles = [{{range $i, $file := .Diff.Files}}{Name:"{{$file.Name}}",NameHash:"{{$file.NameHash}}",Type:{{$file.Type}},IsBin:{{$file.IsBin}},Addition:{{$file.Addition}},Deletion:{{$file.Deletion}},IsViewed:{{$file.IsViewed}}},{{end}}];
 			const diffData = {
@@ -74,7 +63,11 @@
 			window.config.pageData.diffFileInfo = diffFileInfo;
 		</script>
 		<div id="diff-file-list"></div>
+	{{end}}
 	<div id="diff-container">
+		{{if .DiffNotAvailable}}
+			<h4>{{.locale.Tr "repo.diff.data_not_available"}}</h4>
+		{{else}}
 			<div id="diff-file-tree" class="gt-hidden"></div>
 			<script>
 				if (diffTreeVisible) document.getElementById('diff-file-tree').classList.remove('gt-hidden');
@@ -203,9 +196,10 @@
 					</div>
 				{{end}}
 			</div>
+		{{end}}
 	</div>
 
-		{{if not $.Repository.IsArchived}}
+	{{if and (not $.Repository.IsArchived) (not .DiffNotAvailable)}}
 		<template id="issue-comment-editor-template">
 			<div class="ui comment form">
 				{{template "shared/combomarkdowneditor" (dict
@@ -222,7 +216,7 @@
 			</div>
 		</template>
 	{{end}}
-
+	{{if (not .DiffNotAvailable)}}
 		{{template "repo/issue/view_content/reference_issue_dialog" .}}
-	</div>
-{{end}}
+	{{end}}
+</div>

templates/repo/pulls/tab_menu.tmpl

@@ -9,7 +9,7 @@
 		{{$.locale.Tr "repo.pulls.tab_commits"}}
 		<span class="ui small label">{{if .NumCommits}}{{.NumCommits}}{{else}}-{{end}}</span>
 	</a>
-	<a class="item {{if .PageIsPullFiles}}active{{end}}" {{if .NumFiles}}href="{{.Issue.Link}}/files"{{end}}>
+	<a class="item {{if .PageIsPullFiles}}active{{end}}" href="{{.Issue.Link}}/files">
 		{{svg "octicon-diff"}}
 		{{$.locale.Tr "repo.pulls.tab_files"}}
 		<span class="ui small label">{{if .NumFiles}}{{.NumFiles}}{{else}}-{{end}}</span>