fixup! Fix serving files that clash with directories

Try and make things more reasable by seperating assignment from if
conditions and removing early returns.

I still kept assignment in the while condition, because it is a nice and
simple way to assign the first non-"/" string popped off from the path
array.

You should be able to autosquash out this commit, since it is a fixup
commit.

lib/jekyll/commands/serve/servlet.rb

@@ -29,31 +29,38 @@ def search_file(req, res, basename)
         def search_index_file(req, res)
           # /file/index.html -> /file.html
 
-          # First, let's see if the default implementation can figure it out.
-          # (Check for index files in the res.filename directory)
-          if file = super
-            return file
+          # First, let's see if the our super method can figure it out.
+          # (i.e Check for index.html files in the res.filename directory)
+          file = super
+
+          unless file
+            # Ok, I guess that didn't work, I guess there's no basename/index.html
+            # Let's look for basename.html instead...
+
+            # Keep a backup of res.filename in case we need to revert our changes to it
+            old_filename = res.filename
+
+            # We need to calculate the basename and remove it from the path (res.filename)
+            # so we'll turn res.filename into an array of path elements then pop off the
+            # basename.
+            #
+            # We use a while loop just in case res.filename has trailing slashes.
+            #
+            # Once we have popped off the basename, we can join up what's left and use it
+            # as the new res.filename.
+            path_arr = res.filename.scan(%r!/[^/]*!)
+            while basename = path_arr.pop
+              break unless basename == "/"
+            end
+            res.filename = path_arr.join
+
+            # Try and find a file named dirname.html in the parent directory.
+            file = search_file(req, res, basename + ".html")
+
+            # If we didn't find a file, revert our changes to res.filename .
+            res.filename = old_filename unless file
           end
 
-          # Ok, I guess that didn't work, I guess there's no basename/index.html
-          # Let's look for basename.html instead...
-
-          # We need to extract the final part of the path
-          path_arr = res.filename.scan(%r!/[^/]*!)
-          while basename = path_arr.pop
-            break unless basename == "/"
-          end
-
-          # We need to change res.filename to the parent directory for
-          #  search_file to work, so make a backup incase it doesn't work
-          old_filename = res.filename
-          res.filename = path_arr.join
-
-          # Try and find a file named dirname.html in the parent directory
-          unless file = search_file(req, res, basename + ".html")
-            # Don't modify filename unless we actually found a file to serve
-            res.filename = old_filename
-          end
           return file
         end
         # rubocop:enable Lint/AssignmentInCondition