patch 8.2.0551: not all code for options is tested

Problem:    Not all code for options is tested.
Solution:   Add more tests. (Yegappan Lakshmanan, closes #5913)
diff --git a/src/testdir/test_vimscript.vim b/src/testdir/test_vimscript.vim
index 69c9f56..abd0a7e 100644
--- a/src/testdir/test_vimscript.vim
+++ b/src/testdir/test_vimscript.vim
@@ -1411,6 +1411,10 @@
     call assert_equal(["{'a': [1, 2, 3], 'b': [...]}",
 		     \ "{'a': [1, 2, 3], 'b': [1, 2, 3]}"], l)
 
+    call assert_fails('echo &:', 'E112:')
+    call assert_fails('echo &g:', 'E112:')
+    call assert_fails('echo &l:', 'E112:')
+
 endfunc
 
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