[batching] fix subgraph unwrapping (#4849)

Without this fix a null body would cause the router to panic.

With this fix, if a body is null, then the router returns an error to
the user.

apollo-router/src/services/subgraph_service.rs

@@ -805,12 +805,15 @@ pub(crate) async fn process_batch(
     }
 
     tracing::debug!("parts: {parts:?}, content_type: {content_type:?}, body: {body:?}");
-    let value = serde_json::from_slice(&body.unwrap().unwrap()).map_err(|error| {
-        FetchError::SubrequestMalformedResponse {
+    let value =
+        serde_json::from_slice(&body.ok_or(FetchError::SubrequestMalformedResponse {
+            service: service.to_string(),
+            reason: "no body in response".to_string(),
+        })??)
+        .map_err(|error| FetchError::SubrequestMalformedResponse {
             service: service.to_string(),
             reason: error.to_string(),
-        }
-    })?;
+        })?;
 
     tracing::debug!("json value from body is: {value:?}");
 
@@ -1038,7 +1041,7 @@ pub(crate) async fn call_http(
 
     let (parts, _) = subgraph_request.into_parts();
     let body = serde_json::to_string(&body).expect("JSON serialization should not fail");
-    tracing::info!("our JSON body: {body:?}");
+    tracing::debug!("our JSON body: {body:?}");
     let mut request = http::Request::from_parts(parts, Body::from(body));
 
     request