Bug 1411732 - prevent file name tricks for external http attachments. r=jorgk

mail/base/content/msgHdrView.js

@@ -1826,6 +1826,19 @@ function AttachmentInfo(contentType, url, name, uri,
     this.partID = match && match[1];
   }
 
+  // Make sure to communicate it if it's an external http attachment and not a
+  // local attachment. For feeds attachments (enclosures) are always remote,
+  // so there is nothing to communicate.
+  if (isExternalAttachment && url.startsWith("http") &&
+      !gFolderDisplay.selectedMessageIsFeed) {
+    if (this.name) {
+      this.name = url + " - " + this.name;
+    }
+    else {
+      this.name = url;
+    }
+  }
+
   this.url = url;
 }