microformats2: don't crash on raw string values for quotation-of

for snarfed/bridgy#723

thanks for reporting @gRegorLove! this doesn't (yet) fix the whole bug, but it at least prevents the `'unicode' ... has no attribute 'get'` crash.

granary/microformats2.py

@@ -283,7 +283,7 @@ def absolute_urls(prop):
   attachments = [
     json_to_object(quote)
     for quote in mf2.get('children', []) + props.get('quotation-of', [])
-    if 'h-cite' in set(quote.get('type', []))]
+    if isinstance(quote, dict) and 'h-cite' in set(quote.get('type', []))]
 
   obj = {
     'id': prop.get('uid'),

granary/test/testdata/note_with_string_quotation.as-from-mf2.json

@@ -0,0 +1,9 @@
+{
+  "objectType": "note",
+  "content": "i hereby quote",
+  "attachments": [{
+    "objectType": "note",
+    "content": "this is being quoted",
+    "url": "http://quoted/post"
+  }]
+}

granary/test/testdata/note_with_string_quotation.mf2.json

@@ -0,0 +1,16 @@
+{
+  "type": ["h-entry"],
+  "properties": {
+    "content": ["i hereby quote"],
+    "quotation-of": [
+      "this should be ignored",
+      {
+        "type": ["h-cite"],
+        "properties": {
+          "content": ["this is being quoted"],
+          "url": ["http://quoted/post"]
+        }
+      }
+    ]
+  }
+}