autotag: accept files from stdin with '-'.

Fix `autotag` so you can pass a filename of '-' to read a file from
stdin. This way you can do this:

  docker run --rm -i ghcr.io/danbooru/autotagger autotag - < image.jpg

...to perform prediction on a single file outside of Docker.

app.py

@@ -5,7 +5,6 @@ from dotenv import load_dotenv
 from autotagger import Autotagger
 from base64 import b64encode
 from flask import Flask, request, render_template, jsonify
-from fastai.vision.core import PILImage
 
 load_dotenv()
 model_path = getenv("MODEL_PATH", "models/model.pth")
@@ -22,12 +21,11 @@ def index():
 @app.route("/evaluate", methods=["POST"])
 def evaluate():
     files = request.files.getlist("file")
-    images = [PILImage.create(file) for file in files]
     threshold = float(request.form.get("threshold", 0.1))
     output = request.form.get("format", "html")
     limit = int(request.form.get("limit", 50))
 
-    predictions = autotagger.predict(images, threshold=threshold, limit=limit)
+    predictions = autotagger.predict(files, threshold=threshold, limit=limit)
 
     if output == "html":
         for file in files: