Fix IPAddr#== returning true when compared with nil for 0.0.0.0 and ::

Author: taketo1113

lib/ipaddr.rb

@@ -164,6 +164,10 @@ def -(offset)
 
   # Returns true if two ipaddrs are equal.
   def ==(other)
+    if other.nil?
+      return false
+    end
+
     other = coerce_other(other)
   rescue
     false

test/test_ipaddr.rb

@@ -475,6 +475,8 @@ def test_equal
     assert_equal(false, @a != IPAddr.new("3ffe:505:2::"))
     assert_equal(false, @a == @inconvertible_range)
     assert_equal(false, @a == @inconvertible_string)
+    assert_equal(false, IPAddr.new("0.0.0.0") == nil)
+    assert_equal(false, IPAddr.new("::") == nil)
   end
 
   def test_compare