Merge branch 'fix-bulk-assign-labels' into 'master'

Fixes bulk-assign label for multiple issues not having the same labels

## What does this MR do?
Fixes a bug when bulk-assigning a label to multiple issues while the label is present in on the issues on the selection.

## Screenshots (if relevant)

**Before Bugfix**

<img src="/uploads/ad1f290bcf3930177a3a71c69cbe5325/before-bugfix.gif" width="700"/>

**After Bugfix**

<img src="/uploads/1f04d6bf027806fb13ca3773febda744/bugfix.gif" width="700"/>

## Does this MR meet the acceptance criteria?

- [x] Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)

See merge request !4602

app/assets/javascripts/issues-bulk-assignment.js.coffee

@@ -97,13 +97,22 @@ class @IssuableBulkActions
     $labels = @form.find('.labels-filter input[name="update[label_ids][]"]')
 
     $labels.each (k, label) ->
-      labelIds.push $(label).val() if label
+      labelIds.push parseInt($(label).val()) if label
 
     labelIds
 
   ###*
-   * Just an alias of @getUnmarkedIndeterminedLabels
-   * @return {Array} Array of labels
+   * Returns Label IDs that will be removed from issue selection
+   * @return {Array} Array of labels IDs
   ###
   getLabelsToRemove: ->
-    @getUnmarkedIndeterminedLabels()
+    result = []
+    indeterminatedLabels = @getUnmarkedIndeterminedLabels()
+    labelsToApply = @getLabelsToApply()
+
+    indeterminatedLabels.map (id) ->
+      # We need to exclude label IDs that will be applied
+      # By not doing this will cause issues from selection to not add labels at all
+      result.push(id) if labelsToApply.indexOf(id) is -1
+
+    result

spec/features/issues/bulk_assigment_labels_spec.rb

@@ -83,6 +83,23 @@ feature 'Issues > Labels bulk assignment', feature: true do
       end
     end
 
+    context 'can assign a label to all issues when label is present' do
+      before do
+        issue2.labels << bug
+        issue2.labels << feature
+        visit namespace_project_issues_path(project.namespace, project)
+
+        check 'check_all_issues'
+        open_labels_dropdown ['bug']
+        update_issues
+      end
+
+      it do
+        expect(find("#issue_#{issue1.id}")).to have_content 'bug'
+        expect(find("#issue_#{issue2.id}")).to have_content 'bug'
+      end
+    end
+
     context 'can bulk un-assign' do
       context 'all labels to all issues' do
         before do