Fix performance issue in Helm#can_uninstall?

Calling #present? was causing a DB query to happen each time around the
loop. We only wanted to check for nil as it's nil in the first loop
around so there is no need for #present?

app/models/clusters/applications/helm.rb

@@ -41,7 +41,7 @@ module Clusters
 
             extra_apps = Clusters::Applications::Helm.where('EXISTS (?)', klass.select(1).where(cluster_id: cluster_id))
 
-            applications = applications.present? ? applications.or(extra_apps) : extra_apps
+            applications = applications ? applications.or(extra_apps) : extra_apps
           end
 
           !applications.exists?

spec/models/clusters/applications/helm_spec.rb

@@ -23,7 +23,7 @@ describe Clusters::Applications::Helm do
       Clusters::Cluster::APPLICATIONS.keys.each do |application_name|
         next if application_name == 'helm'
 
-        it do
+        it "is false when #{application_name} is installed" do
           cluster_application = create("clusters_applications_#{application_name}".to_sym)
 
           helm = cluster_application.cluster.application_helm
@@ -31,6 +31,14 @@ describe Clusters::Applications::Helm do
           expect(helm.allowed_to_uninstall?).to be_falsy
         end
       end
+
+      it 'executes a single query only' do
+        cluster_application = create(:clusters_applications_ingress)
+        helm = cluster_application.cluster.application_helm
+
+        query_count = ActiveRecord::QueryRecorder.new { helm.allowed_to_uninstall? }.count
+        expect(query_count).to eq(1)
+      end
     end
 
     context "without other existing applications" do