[zerochan] normalize "No results" output message (#8313)

catch and handle '404 Not Found' responses

test/results/zerochan.py

@@ -45,6 +45,13 @@ __tests__ = (
     "width"      : r"re:^\d+$",
 },
 
+{
+    "#url"     : "https://www.zerochan.net/non_existant_tag",
+    "#comment" : "handle HttpError exception (#8313)",
+    "#class"   : zerochan.ZerochanTagExtractor,
+    "#count"   : 0,
+},
+
 {
     "#url"     : "https://www.zerochan.net/2920445",
     "#category": ("booru", "zerochan", "image"),
@@ -341,4 +348,20 @@ __tests__ = (
     ],
 },
 
+{
+    "#url"     : "https://www.zerochan.net/1",
+    "#category": ("booru", "zerochan", "image"),
+    "#class"   : zerochan.ZerochanImageExtractor,
+    "#count"   : 0,
+    "#log"     : "'deleted'",
+},
+
+{
+    "#url"     : "https://www.zerochan.net/9876540",
+    "#category": ("booru", "zerochan", "image"),
+    "#class"   : zerochan.ZerochanImageExtractor,
+    "#count"   : 0,
+    "#log"     : "'Not found'",
+},
+
 )