Handle blank file path in UploadedFile.from_params

https://gitlab.com/gitlab-org/security/gitlab-workhorse/-/merge_requests/3
changed Workhorse so that it always provided `file.path` when
`direct_upload` was enabled, even if that path was blank.

Whereas we were checking for `path` not being `nil`, we now need to
check that it's present.

See also https://gitlab.com/gitlab-org/gitlab/-/issues/212424

lib/uploaded_file.rb

@@ -48,7 +48,7 @@ class UploadedFile
     return if path.blank? && remote_id.blank?
 
     file_path = nil
-    if path
+    if path.present?
       file_path = File.realpath(path)
 
       paths = Array(upload_paths) << Dir.tmpdir

spec/lib/uploaded_file_spec.rb

@@ -59,6 +59,16 @@ describe UploadedFile do
           expect(subject.sha256).to eq('sha256')
           expect(subject.remote_id).to eq('remote_id')
         end
+
+        it 'handles a blank path' do
+          params['file.path'] = ''
+
+          # Not a real file, so can't determine size itself
+          params['file.size'] = 1.byte
+
+          expect { described_class.from_params(params, :file, upload_path) }
+            .not_to raise_error
+        end
       end
     end