iqdb: fix error with file uploads.

Fix "cannot determine size of body" errors on upload page. Caused by
exception during IQDB lookup. We were posting the form data wrong, we
need to wrap the file with HTTP::FormData::File and pass it through the
`form` parameter.

app/logical/iqdb_proxy.rb

@@ -50,9 +50,12 @@ class IqdbProxy
     file.try(:close)
   end
 
-  def query(params)
+  def query(file: nil, url: nil, limit: 20)
     raise NotImplementedError, "the IQDBs service isn't configured" unless enabled?
-    response = http.post("#{iqdbs_server}/similar", body: params)
+
+    file = HTTP::FormData::File.new(file) if file
+    form = { file: file, url: url, limit: limit }.compact
+    response = http.post("#{iqdbs_server}/similar", form: form)
 
     raise Error, "IQDB error: #{response.status}" if response.status != 200
     raise Error, "IQDB error: #{response.parse["error"]}" if response.parse.is_a?(Hash)