Fix Renderer errors with --enable-frozen-string-literal

There were several instances in which adding .b to string literals was
necessary to not throw this error when --enable-frozen-string-literal
was enabled. Exposed with tests.

lib/combine_pdf/renderer.rb

@@ -101,15 +101,15 @@ def format_hash_to_pdf(object)
         end
         object[:indirect_reference_id] ||= 0
         object[:indirect_generation_number] ||= 0
-        return "#{object[:indirect_reference_id]} #{object[:indirect_generation_number]} R".force_encoding(Encoding::ASCII_8BIT)
+        return "#{object[:indirect_reference_id]} #{object[:indirect_generation_number]} R".b.force_encoding(Encoding::ASCII_8BIT)
       end
 
       # if the object is indirect...
       out = []
       if object[:indirect_reference_id]
         object[:indirect_reference_id] ||= 0
         object[:indirect_generation_number] ||= 0
-        out << "#{object[:indirect_reference_id]} #{object[:indirect_generation_number]} obj\n".force_encoding(Encoding::ASCII_8BIT)
+        out << "#{object[:indirect_reference_id]} #{object[:indirect_generation_number]} obj\n".b.force_encoding(Encoding::ASCII_8BIT)
         if object[:indirect_without_dictionary]
           out << object_to_pdf(object[:indirect_without_dictionary])
           out << "\nendobj\n"
@@ -126,11 +126,11 @@ def format_hash_to_pdf(object)
       # (using LESS-THAN SIGNs (3Ch) and GREATER-THAN SIGNs (3Eh)).
       out << "<<\n".b
       object.each do |key, value|
-        out << "#{object_to_pdf key} #{object_to_pdf value}\n".force_encoding(Encoding::ASCII_8BIT) unless PDF::PRIVATE_HASH_KEYS.include? key
+        out << "#{object_to_pdf key} #{object_to_pdf value}\n".b.force_encoding(Encoding::ASCII_8BIT) unless PDF::PRIVATE_HASH_KEYS.include? key
       end
       object.delete :Length
       out << '>>'.b
-      out << "\nstream\n#{object[:raw_stream_content]}\nendstream".force_encoding(Encoding::ASCII_8BIT) if object[:raw_stream_content]
+      out << "\nstream\n#{object[:raw_stream_content]}\nendstream".b.force_encoding(Encoding::ASCII_8BIT) if object[:raw_stream_content]
       out << "\nendobj\n" if object[:indirect_reference_id]
       out.join.force_encoding(Encoding::ASCII_8BIT)
     end

test/combine_pdf/renderer_test.rb

@@ -17,4 +17,30 @@ def test_numeric_array_to_pdf
 
     assert_equal(expected, actual)
   end
+
+  def test_object_to_pdf_indirect_reference_id
+    actual = TestRenderer.new.test_object(
+      :indirect_reference_id => 1,
+      :indirect_generation_number => 2
+    )
+    assert_match /^1 2 obj/, actual
+    assert_match /endobj$/, actual
+  end
+
+  def test_object_to_pdf_is_reference_only
+    actual = TestRenderer.new.test_object(
+      :Pages => {
+        :referenced_object => { :Type => :Pages, :Count => 0, :indirect_reference_id => 3 },
+        :is_reference_only => true
+      }
+    )
+    assert_match /Pages 3 0 R/, actual
+  end
+
+  def test_object_to_pdf_raw_stream_content
+    actual = TestRenderer.new.test_object(
+      :raw_stream_content => 'Testing'
+    )
+    assert_match /stream\nTesting\nendstream/, actual
+  end
 end