Avoid parsing a path into // when there's no host

This avoids a contradiction where the URL starts out with no host,
but gets normalized into a URL where the first part of a path is
interpreted as the host.

Fixes #397

Author: zealousidealroll

src/parser.rs

@@ -1045,7 +1045,7 @@ impl<'a> Parser<'a> {
                             *has_host = false;  // FIXME account for this in callers
                         }
                     }
-                    if ends_with_slash {
+                    if ends_with_slash && (*has_host || &self.serialization[path_start..] != "/") {
                         self.serialization.push('/')
                     }
                 }

tests/urltestdata.json

@@ -6144,5 +6144,20 @@
     "pathname": "/test",
     "search": "?a",
     "hash": "#bc"
+  },
+  "Found by fuzzing",
+  {
+    "input": "a:/a/..//a",
+    "base": "about:blank",
+    "href": "a:/a",
+    "protocol": "a:",
+    "username": "",
+    "password": "",
+    "host": "",
+    "hostname": "",
+    "port": "",
+    "pathname": "/a",
+    "search": "",
+    "hash": ""
   }
 ]