Fix comparison with Version::NULL on RHS

This was accounted for in Version::NULL.<=>, but not in Version#<=>,
so these could only be compared if Version::NULL was the left hand
side.

The check had to go above the check that `other` is a version because
`Version::NULL`'s anonymous class does not inherit from `Version`.
(The type check feels like it's probably a smell, but out of scope).

Library/Homebrew/test/version_spec.rb

@@ -144,6 +144,10 @@ describe Version do
     expect(described_class.create("2.1.0-p194")).to be > nil
   end
 
+  it "can be compared against Version::NULL" do
+    expect(described_class.create("2.1.0-p194")).to be > Version::NULL
+  end
+
   it "can be compared against strings" do
     expect(described_class.create("2.1.0-p194")).to be == "2.1.0-p194"
     expect(described_class.create("1")).to be == 1

Library/Homebrew/version.rb

@@ -387,6 +387,7 @@ class Version
     other = Version.new(other.to_s) if other.is_a? Integer
     return 1 if other.nil?
 
+    return 1 if other.respond_to?(:null?) && other.null?
     return unless other.is_a?(Version)
     return 0 if version == other.version
     return 1 if head? && !other.head?