Fix/header_check_fix_2 (#880)

* dont assume field

* check better

lnbits/app.py

@@ -76,7 +76,11 @@ def create_app(config_object="lnbits.settings") -> FastAPI:
         # Only the browser sends "text/html" request
         # not fail proof, but everything else get's a JSON response
 
-        if request.headers and "text/html" in request.headers["accept"]:
+        if (
+            request.headers
+            and "accept" in request.headers
+            and "text/html" in request.headers["accept"]
+        ):
             return template_renderer().TemplateResponse(
                 "error.html",
                 {"request": request, "err": f"{exc.errors()} is not a valid UUID."},
@@ -197,7 +201,11 @@ def register_exception_handlers(app: FastAPI):
         traceback.print_exception(etype, err, tb)
         exc = traceback.format_exc()
 
-        if request.headers and "text/html" in request.headers["accept"]:
+        if (
+            request.headers
+            and "accept" in request.headers
+            and "text/html" in request.headers["accept"]
+        ):
             return template_renderer().TemplateResponse(
                 "error.html", {"request": request, "err": err}
             )