Do not validate .model.json files with no content/whitespace only (#420)

* Ignore empty/whitespace-only model.json files

* Ignore no return value from model.json files during snapshot

* Use str::from_utf8 instead of String::from_utf8

* Revert "Ignore no return value from model.json files during snapshot"

This reverts commit 0aef16e30a.

* Add test for empty .model.json files

* Change empty .model.json check method

Co-authored-by: Lucien Greathouse <me@lpghatguy.com>

* Format code with cargo fmt

* Use raw string instead

Co-authored-by: Lucien Greathouse <me@lpghatguy.com>

rojo-test/serve-test-snapshots/end_to_end__tests__serve__empty_json_model_all-2.snap

@@ -0,0 +1,28 @@
+---
+source: tests/tests/serve.rs
+expression: "read_response.intern_and_redact(&mut redactions, root_id)"
+
+---
+instances:
+  id-2:
+    Children:
+      - id-3
+    ClassName: Folder
+    Id: id-2
+    Metadata:
+      ignoreUnknownInstances: false
+    Name: empty_folder
+    Parent: "00000000000000000000000000000000"
+    Properties: {}
+  id-3:
+    Children: []
+    ClassName: Model
+    Id: id-3
+    Metadata:
+      ignoreUnknownInstances: false
+    Name: test
+    Parent: id-2
+    Properties: {}
+messageCursor: 1
+sessionId: id-1
+

rojo-test/serve-test-snapshots/end_to_end__tests__serve__empty_json_model_all.snap

@@ -0,0 +1,18 @@
+---
+source: tests/tests/serve.rs
+expression: "read_response.intern_and_redact(&mut redactions, root_id)"
+
+---
+instances:
+  id-2:
+    Children: []
+    ClassName: Folder
+    Id: id-2
+    Metadata:
+      ignoreUnknownInstances: false
+    Name: empty_folder
+    Parent: "00000000000000000000000000000000"
+    Properties: {}
+messageCursor: 0
+sessionId: id-1
+

rojo-test/serve-test-snapshots/end_to_end__tests__serve__empty_json_model_info.snap

@@ -0,0 +1,14 @@
+---
+source: tests/tests/serve.rs
+expression: redactions.redacted_yaml(info)
+
+---
+expectedPlaceIds: ~
+gameId: ~
+placeId: ~
+projectName: empty_folder
+protocolVersion: 4
+rootInstanceId: id-2
+serverVersion: "[server-version]"
+sessionId: id-1
+

rojo-test/serve-test-snapshots/end_to_end__tests__serve__empty_json_model_subscribe.snap

@@ -0,0 +1,21 @@
+---
+source: tests/tests/serve.rs
+expression: "subscribe_response.intern_and_redact(&mut redactions, ())"
+
+---
+messageCursor: 1
+messages:
+  - added:
+      id-3:
+        Children: []
+        ClassName: Model
+        Id: id-3
+        Metadata:
+          ignoreUnknownInstances: false
+        Name: test
+        Parent: id-2
+        Properties: {}
+    removed: []
+    updated: []
+sessionId: id-1
+

rojo-test/serve-tests/empty_json_model/default.project.json

@@ -0,0 +1,6 @@
+{
+  "name": "empty_folder",
+  "tree": {
+    "$path": "src"
+  }
+}