Fix SanitizedFile#move_to wrongly detects content_type based on the path before move

Fixes #2495, Closes #2496

Author: mshibuya

lib/carrierwave/sanitized_file.rb

@@ -182,9 +182,9 @@ def move_to(new_path, permissions=nil, directory_permissions=nil, keep_filename=
       move!(new_path)
       chmod!(new_path, permissions)
       if keep_filename
-        self.file = {:tempfile => new_path, :filename => original_filename, :content_type => content_type}
+        self.file = {:tempfile => new_path, :filename => original_filename, :content_type => @content_type}
       else
-        self.file = {:tempfile => new_path, :content_type => content_type}
+        self.file = {:tempfile => new_path, :content_type => @content_type}
       end
       self
     end

spec/sanitized_file_spec.rb

@@ -371,10 +371,18 @@
         expect(sanitized_file.move_to(file_path("gurr.png"))).to eq(sanitized_file)
       end
 
-      it "should convert the file's content type" do
+      it "should preserve the file's content type" do
+        sanitized_file.content_type = 'application/octet-stream'
+        sanitized_file.move_to(file_path("new_dir","gurr.png"))
+
+        expect(sanitized_file.content_type).to eq("application/octet-stream")
+      end
+
+      it "should detect content type correctly using MagicMime when content_type is not set" do
+        sanitized_file.content_type = nil
         sanitized_file.move_to(file_path("new_dir","gurr.png"))
 
-        expect(sanitized_file.content_type).to eq("image/jpeg")
+        expect(sanitized_file.content_type).to eq("invalid/invalid")
       end
 
       context 'target path only differs by case' do