fix: prevent backspace from deleting files when text contains whitespace (#10261)

- Change condition from text.trim() === '' to text.length === 0
- Users can now delete whitespace characters (spaces, tabs, newlines) without accidentally deleting attached files
- File deletion only occurs when text is completely empty
- Maintains existing functionality for file deletion when text is truly empty

Fixes: Blank character input causes backspace to incorrectly delete attached images

Signed-off-by: zhaokun <zhaokun_zhang@icloud.com>

src/renderer/src/pages/home/Inputbar/Inputbar.tsx

@@ -377,7 +377,7 @@ const Inputbar: FC<Props> = ({ assistant: _assistant, setActiveTopic, topic }) =
       }
     }
 
-    if (event.key === 'Backspace' && text.trim() === '' && files.length > 0) {
+    if (event.key === 'Backspace' && text.length === 0 && files.length > 0) {
       setFiles((prev) => prev.slice(0, -1))
       return event.preventDefault()
     }