Allow preview for empty body in ExtendedTextarea

Instead of disabling the preview feature when the body is empty, we show
`Nothing to preview`

src/components/ExtendedTextarea.svelte

@@ -231,7 +231,11 @@
 <div class="comment-section" aria-label="extended-textarea" class:inline>
   {#if preview}
     <div class="preview">
-      <Markdown {rid} breaks content={body} />
+      {#if body.trim().length === 0}
+        <span class="txt-missing">Nothing to preview.</span>
+      {:else}
+        <Markdown {rid} breaks content={body} />
+      {/if}
     </div>
   {:else}
     <Textarea
@@ -277,10 +281,7 @@
         <Icon name="attachment" />
         Attach
       </OutlineButton>
-      <OutlineButton
-        variant="ghost"
-        disabled={body.trim() === ""}
-        onclick={() => (preview = !preview)}>
+      <OutlineButton variant="ghost" onclick={() => (preview = !preview)}>
         <Icon name={preview ? "pen" : "eye"} />
         {preview ? "Edit" : "Preview"}
       </OutlineButton>

src/views/repo/CreateIssue.svelte

@@ -101,7 +101,11 @@
   <div class="content">
     {#if preview}
       <div class="title">
-        <InlineTitle content={title} fontSize="medium" />
+        {#if title.trim().length === 0}
+          <span class="txt-missing">No title</span>
+        {:else}
+          <InlineTitle content={title} fontSize="medium" />
+        {/if}
       </div>
     {:else}
       <div style:margin-bottom="1rem">