Prepend AppSubUrl to links for default avatar (#15341)

Fix #15334

Signed-off-by: Andrew Thornton <art27@cantab.net>

templates/repo/diff/comments.tmpl

@@ -3,7 +3,7 @@
 {{ $createdStr:= TimeSinceUnix .CreatedUnix $.root.Lang }}
 <div class="comment" id="{{.HashTag}}">
 	{{if .OriginalAuthor }}
-		<span class="avatar"><img src="/img/avatar_default.png"></span>
+		<span class="avatar"><img src="{{AppSubUrl}}/img/avatar_default.png"></span>
 	{{else}}
 		<a class="avatar" {{if gt .Poster.ID 0}}href="{{.Poster.HomeLink}}"{{end}}>
 			{{avatar .Poster}}

templates/repo/issue/view_content.tmpl

@@ -13,7 +13,7 @@
 		<ui class="ui timeline">
 			<div id="{{.Issue.HashTag}}" class="timeline-item comment first">
 			{{if .Issue.OriginalAuthor }}
-				<span class="timeline-avatar"><img src="/img/avatar_default.png"></span>
+				<span class="timeline-avatar"><img src="{{AppSubUrl}}/img/avatar_default.png"></span>
 			{{else}}
 				<a class="timeline-avatar" {{if gt .Issue.Poster.ID 0}}href="{{.Issue.Poster.HomeLink}}"{{end}}>
 					{{avatar .Issue.Poster}}

templates/repo/issue/view_content/comments.tmpl

@@ -8,12 +8,12 @@
 	 18 = REMOVED_DEADLINE, 19 = ADD_DEPENDENCY, 20 = REMOVE_DEPENDENCY, 21 = CODE,
 	 22 = REVIEW, 23 = ISSUE_LOCKED, 24 = ISSUE_UNLOCKED, 25 = TARGET_BRANCH_CHANGED,
 	 26 = DELETE_TIME_MANUAL, 27 = REVIEW_REQUEST, 28 = MERGE_PULL_REQUEST,
-	 29 = PULL_PUSH_EVENT, 30 = PROJECT_CHANGED, 31 = PROJECT_BOARD_CHANGED 
+	 29 = PULL_PUSH_EVENT, 30 = PROJECT_CHANGED, 31 = PROJECT_BOARD_CHANGED
 	 32 = DISMISSED_REVIEW -->
 	{{if eq .Type 0}}
 		<div class="timeline-item comment" id="{{.HashTag}}">
 		{{if .OriginalAuthor }}
-			<span class="timeline-avatar"><img src="/img/avatar_default.png"></span>
+			<span class="timeline-avatar"><img src="{{AppSubUrl}}/img/avatar_default.png"></span>
 		{{else}}
 			<a class="timeline-avatar" {{if gt .Poster.ID 0}}href="{{.Poster.HomeLink}}"{{end}}>
 				{{avatar .Poster}}