Avoid duplicated sections in a generated TODO file (additional fix)

spec/ameba/formatter/todo_formatter_spec.cr

@@ -82,6 +82,7 @@ module Ameba
         s1 = Source.new "a = 1", "source1.cr"
         s2 = Source.new "a = 1", "source2.cr"
         s1.add_issue DummyRule.new, {1, 2}, "message1"
+        s1.add_issue NamedRule.new, {1, 2}, "message1"
         s1.add_issue DummyRule.new, {2, 2}, "message1"
         s2.add_issue DummyRule.new, {2, 2}, "message2"
 

src/ameba/formatter/todo_formatter.cr

@@ -41,8 +41,7 @@ module Ameba::Formatter
       Hash(Rule::Base, Array(Issue)).new.tap do |h|
         issues.each do |issue|
           next if issue.disabled? || issue.rule.is_a? Rule::Lint::Syntax
-          h[issue.rule] ||= Array(Issue).new
-          h[issue.rule] << issue
+          (h[issue.rule] ||= Array(Issue).new) << issue
         end
       end
     end

src/ameba/rule/base.cr

@@ -106,7 +106,11 @@ module Ameba::Rule
     end
 
     def ==(other)
-      self.name == other.name
+      name == other.try &.name
+    end
+
+    def hash
+      name.hash
     end
 
     macro issue_for(*args)