Merge pull request #417 from theSlyest/fix_request_with_empty_fields_list

Fix Request with empty list of fields crash bug

Author: WolfgangSenff

addons/godot-firebase/firestore/firestore_document.gd

@@ -21,7 +21,8 @@ signal changed(changes)
 func _init(doc : Dictionary = {}):
 	_transforms = FieldTransformArray.new()
 
-	document = doc.fields
+	if doc.has("fields"):
+		document = doc.fields
 	doc_name = doc.name
 	if doc_name.count("/") > 2:
 		doc_name = (doc_name.split("/") as Array).back()