(#22214): close content file before executing checkscript

Right now validation seems to be done against zero byte generated temp
files. We need to close the file before executing validation against it.

lib/puppet/parser/functions/validate_cmd.rb

@@ -32,6 +32,7 @@ module Puppet::Parser::Functions
     tmpfile = Tempfile.new("validate_cmd")
     begin
       tmpfile.write(content)
+      tmpfile.close
       if Puppet::Util::Execution.respond_to?('execute')
         Puppet::Util::Execution.execute("#{checkscript} #{tmpfile.path}")
       else

spec/unit/puppet/parser/functions/validate_cmd_spec.rb

@@ -78,4 +78,12 @@ describe Puppet::Parser::Functions.function(:validate_cmd) do
       end
     end
   end
+
+  it "can positively validate file content" do
+    expect { subject.call ["non-empty", "/usr/bin/test -s"] }.to_not raise_error
+  end
+
+  it "can negatively validate file content" do
+    expect { subject.call ["", "/usr/bin/test -s"] }.to raise_error Puppet::ParseError, /failed to validate.*test -s/
+  end
 end