fish: validate clone inputs

fish/functions/clone.fish

@@ -1,4 +1,9 @@
 function clone --argument-names giturl
+    if test (count $argv) -gt 1
+        echo "Expected a Git URL but got "(count $argv)" arguments: '$argv'"
+        return 1
+    end
+
     # These regular expressions are far from comprehensive, but they work for me.
     #
     # Examples: