ui/vnc-clipboard: fix inflate_buffer

Commit d921fea338 ("ui/vnc-clipboard: fix infinite loop in
inflate_buffer (CVE-2023-3255)") removed this hunk, but it is still
required, because it can happen that stream.avail_in becomes zero
before coming across a return value of Z_STREAM_END in the loop.

This fixes the host->guest direction of the clipboard with noVNC and
TigerVNC as clients.

Fixes: d921fea338 ("ui/vnc-clipboard: fix infinite loop in inflate_buffer (CVE-2023-3255)")
Reported-by: Friedrich Weber <f.weber@proxmox.com>
Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
Acked-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20231122125826.228189-1-f.ebner@proxmox.com>

ui/vnc-clipboard.c

@@ -69,6 +69,11 @@ static uint8_t *inflate_buffer(uint8_t *in, uint32_t in_len, uint32_t *size)
         }
     }
 
+    *size = stream.total_out;
+    inflateEnd(&stream);
+
+    return out;
+
 err_end:
     inflateEnd(&stream);
 err: