`delphi` endpoint returns wrong result code
When there are no results, Epidata should return
```
{"result":-2, "message":"no results", "epidata": []}
```

But for the `delphi` endpoint, we're returning the following, causing `Epidata.check` to fail to identify the no-results condition:
```
$ curl -sL "http://api.covidcast.cmu.edu/epidata/delphi/?system=epic&epiweek=202132"
{"epidata":[],"message":"success","result":1}
$ curl -sL "http://api.covidcast.cmu.edu/epidata/api.php?source=delphi&system=epic&epiweek=202132"
{"epidata":[],"message":"success","result":1}
```

This in turn is causing excessive (multi-hour) runtimes on some of the nowcasting sensor updates.
diff --git a/src/server/_printer.py b/src/server/_printer.py
index 06f92b42..715214e1 100644
--- a/src/server/_printer.py
+++ b/src/server/_printer.py
@@ -18,8 +18,16 @@ def print_non_standard(data):
     format = request.values.get("format", "classic")
     if format == "json":
         return jsonify(data)
+
+    if not data:
+        message = "no results"
+        result = -2
     else:
-        return jsonify(dict(result=1, message="success", epidata=data))
+        message = "success"
+        result = 1
+    if result == -1 and is_compatibility_mode():
+        return jsonify(dict(result=result, message=message))
+    return jsonify(dict(result=result, message=message, epidata=data))
 
 
 class APrinter:
['src/server/_printer.py']