converters/h: Work around an issue and clean up the code

Ref: #128

lib/coradoc/input/html/converters/base.rb

@@ -10,19 +10,19 @@ def convert(node, state = {})
 
       # Note: treat_children won't run plugin hooks
       def treat_children(node, state)
-        node.children.inject("") do |memo, child|
-          memo << treat(child, state)
-        end
+        node.children.map do |child|
+          treat(child, state)
+        end.join
       end
 
       def treat(node, state)
         Converters.process(node, state)
       end
 
       def treat_children_coradoc(node, state)
-        node.children.inject([]) do |memo, child|
-          memo << treat_coradoc(child, state)
-        end.flatten.reject { |x| x == "" || x.nil? }
+        node.children.map do |child|
+          treat_coradoc(child, state)
+        end.flatten.reject { |x| x.to_s.empty? }
       end
 
       def treat_coradoc(node, state)

lib/coradoc/input/html/converters/h.rb

@@ -6,7 +6,9 @@ def to_coradoc(node, state = {})
         internal_anchor = treat_children_anchors(node, state)
 
         if id.to_s.empty? && internal_anchor.size.positive?
-          id = internal_anchor.first.id
+          if internal_anchor.first.respond_to? :id
+            id = internal_anchor.first.id
+          end
         end
 
         level = node.name[/\d/].to_i
@@ -16,14 +18,14 @@ def to_coradoc(node, state = {})
       end
 
       def treat_children_no_anchors(node, state)
-        node.children.reject { |a| a.name == "a" }.inject([]) do |memo, child|
-          memo << treat_coradoc(child, state)
+        node.children.reject { |a| a.name == "a" }.map do |child|
+          treat_coradoc(child, state)
         end
       end
 
       def treat_children_anchors(node, state)
-        node.children.select { |a| a.name == "a" }.inject([]) do |memo, child|
-          memo << treat_coradoc(child, state)
+        node.children.select { |a| a.name == "a" }.map do |child|
+          treat_coradoc(child, state)
         end
       end
     end