Fix #3395: fix pixiv API exception when uploading bad pixiv id images.

Fixes an exception when attempting to upload a Pixiv image from a
deleted work. The download strategy tries to fetch the source data in
the course of rewriting the URL, which fails if the work has been
deleted from Pixiv.

Raise a BadIDError and leave the URL as-is (don't rewrite it).

test/unit/downloads/pixiv_test.rb

@@ -43,8 +43,6 @@ module Downloads
         end
       end
 
-
-
       # Test a new illustration (one uploaded after 2014-09-30). New illustrations
       # must use /img-original/ for full size URLs. Old /imgXX/img/username/ style URLs
       # don't work for images uploaded after this date.
@@ -112,6 +110,27 @@ module Downloads
         end
       end
 
+      context "downloading a bad id image" do
+        setup do
+          @bad_id_full   = "https://i.pximg.net/img-original/img/2017/11/22/01/06/44/65991677_p0.png"
+          @bad_id_sample = "https://i.pximg.net/c/600x600/img-master/img/2017/11/22/01/06/44/65991677_p0_master1200.jpg"
+        end
+
+        should "not raise an error when rewriting the url" do
+          assert_nothing_raised { assert_not_rewritten(@bad_id_full) }
+        end
+
+        should_eventually "rewrite bad id samples to full size" do
+          assert_rewritten(@bad_id_full, @bad_id_sample)
+        end
+
+        # XXX This may fail someday. Pixiv doesn't delete bad id images right
+        # away, but they may be deleted eventually.
+        should "download the image" do
+          assert_downloaded(21440, @bad_id_full)
+        end
+      end
+
       context "downloading a ugoira" do
         setup do
           @medium_page     = "http://www.pixiv.net/member_illust.php?mode=medium&illust_id=62247364"

test/unit/sources/pixiv_test.rb

@@ -127,6 +127,14 @@ module Sources
         end        
       end
 
+      context "fetching source data for a deleted work" do
+        should "raise a bad id error" do
+          assert_raise(::PixivApiClient::BadIDError) do
+            get_source("https://i.pximg.net/img-original/img/2017/11/22/01/06/44/65991677_p0.png")
+          end
+        end
+      end
+
       context "fetching the commentary" do
         should "work when the description is blank" do
           get_source("https://www.pixiv.net/member_illust.php?mode=medium&illust_id=65981746")