patch 9.0.1846: [security] crash in fullcommand

Problem:  crash in fullcommand
Solution: Check for typeval correctly

Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/ex_docmd.c b/src/ex_docmd.c
index 32d52ab..10d979d 100644
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -4087,7 +4087,7 @@
 		|| check_for_opt_bool_arg(argvars, 1) == FAIL))
 	return;
 
-    name = argvars[0].vval.v_string;
+    name = tv_get_string(&argvars[0]);
     if (name == NULL)
 	return;