patch 8.2.2133: Vim9: checking for a non-empty string is too strict

Problem:    Vim9: checking for a non-empty string is too strict.
Solution:   Check for any string. (closes #7447)
diff --git a/src/typval.c b/src/typval.c
index 64112e7..affd668 100644
--- a/src/typval.c
+++ b/src/typval.c
@@ -341,14 +341,12 @@
 #endif
 
 /*
- * Give an error and return FAIL unless "tv" is a non-empty string.
+ * Give an error and return FAIL unless "tv" is a string.
  */
     int
 check_for_string(typval_T *tv)
 {
-    if (tv->v_type != VAR_STRING
-	    || tv->vval.v_string == NULL
-	    || *tv->vval.v_string == NUL)
+    if (tv->v_type != VAR_STRING)
     {
 	emsg(_(e_stringreq));
 	return FAIL;
@@ -357,6 +355,22 @@
 }
 
 /*
+ * Give an error and return FAIL unless "tv" is a non-empty string.
+ */
+    int
+check_for_nonempty_string(typval_T *tv)
+{
+    if (check_for_string(tv) == FAIL)
+	return FAIL;
+    if (tv->vval.v_string == NULL || *tv->vval.v_string == NUL)
+    {
+	emsg(_(e_non_empty_string_required));
+	return FAIL;
+    }
+    return OK;
+}
+
+/*
  * Get the string value of a variable.
  * If it is a Number variable, the number is converted into a string.
  * tv_get_string() uses a single, static buffer.  YOU CAN ONLY USE IT ONCE!