Better handle label references that aren't actually references

Fixes #1690

lib/gitlab/markdown/label_reference_filter.rb

@@ -84,11 +84,11 @@ module Gitlab
       #
       # Returns a Hash.
       def label_params(id, name)
-        if id > 0
-          { id: id }
-        else
+        if name
           # TODO (rspeicher): Don't strip single quotes if we decide to only use double quotes for surrounding.
           { name: name.tr('\'"', '') }
+        else
+          { id: id }
         end
       end
     end

spec/lib/gitlab/markdown/label_reference_filter_spec.rb

@@ -149,5 +149,12 @@ module Gitlab::Markdown
         end
       end
     end
+
+    describe 'edge cases' do
+      it 'gracefully handles non-references matching the pattern' do
+        exp = act = '(format nil "~0f" 3.0) ; 3.0'
+        expect(filter(act).to_html).to eq exp
+     end
+    end
   end
 end