patch 8.1.0651: :args \"foo works like :args without argument

Problem:    :args \"foo works like :args without argument.
Solution:   Fix check for empty argument. (closes #3728)
diff --git a/src/testdir/test_arglist.vim b/src/testdir/test_arglist.vim
index cb1117e..72e727f 100644
--- a/src/testdir/test_arglist.vim
+++ b/src/testdir/test_arglist.vim
@@ -217,6 +217,12 @@
   %argdelete
 endfunc
 
+func Test_args_with_quote()
+  args \"foobar
+  call assert_equal('"foobar', argv(0))
+  %argdelete
+endfunc
+
 " Test for 0argadd and 0argedit
 " Ported from the test_argument_0count.in test script
 func Test_zero_argadd()