importer: fix frontmatter md dates not imported properly

Signed-off-by: DidierLmn <DidierLmn@users.noreply.github.com>

Author: DidierLmn

packages/core/__tests__/data/md/md-with-frontmatter.md

@@ -3,6 +3,8 @@ title: A beautiful morning
 tags: wonderful,journal
 pinned: true
 favorite: true
+created_at: 2013-06-06T09:00:00.001Z
+updated_at: 2014-05-16T10:30:00.001Z
 ---
 
 # An h1 header

packages/core/src/providers/md/index.ts

@@ -63,16 +63,22 @@ export class Markdown implements IFileProvider<MarkdownSettings> {
       );
       note.pinned = frontmatter.pinned;
       note.favorite = frontmatter.favorite;
-      note.dateCreated = getPropertyWithFallbacks(
+      const dateCreated = getPropertyWithFallbacks(
         frontmatter,
         ["created", "created_at", "date created"],
         note.dateCreated
       );
-      note.dateEdited = getPropertyWithFallbacks(
+      if (dateCreated !== undefined) {
+        note.dateCreated = new Date(dateCreated).getTime();
+      }
+      const dateEdited = getPropertyWithFallbacks(
         frontmatter,
         ["updated", "updated_at", "date updated"],
         note.dateEdited
       );
+      if (dateEdited !== undefined) {
+        note.dateEdited = new Date(dateEdited).getTime();
+      }
       note.color = frontmatter.color;
     }
     yield { type: "note", note };