Ensure size param is set for a disk

plugins/kernel_v2/config/disk.rb

@@ -169,11 +169,12 @@ module VagrantPlugins
           if @size.is_a?(String)
             @size = Vagrant::Util::Numeric.string_to_bytes(@size)
           end
+        end
 
         if !@size
           errors << I18n.t("vagrant.config.disk.invalid_size", name: @name, machine: machine.name)
         end
-        end
+
 
         if @file
           if !@file.is_a?(String)

test/unit/plugins/kernel_v2/config/disk_test.rb

@@ -56,6 +56,16 @@ describe VagrantPlugins::Kernel_V2::VagrantConfigDisk do
     end
   end
 
+  describe "with an invalid config" do
+    let(:invalid_subject) { described_class.new(type) }
+
+    it "raises an error if size not set" do
+      invalid_subject.name = "bar"
+      subject.finalize!
+      assert_invalid
+    end
+  end
+
   describe "defining a new config that needs to match internal restraints" do
     before do
     end