Fix divide by zero

app.py

@@ -165,11 +165,15 @@ def bot(history):
             response.append(elm)
             history[-1][1] = prefix + "".join(response)
             yield history
-
-    _ = (
-        f"(time elapsed: {atime.duration_human}, "  # type: ignore
-        f"{atime.duration/len(''.join(response)):.2f}s/char)"  # type: ignore
-    )
+    if response:
+        _ = (
+            f"(time elapsed: {atime.duration_human}, "  # type: ignore
+            f"{atime.duration/len(''.join(response)):.2f}s/char)"  # type: ignore
+        )
+    else:
+        _ = (
+            f"(time elapsed: {atime.duration_human})"  # type: ignore
+        )
 
     history[-1][1] = "".join(response) + f"\n{_}"
     yield history