patch 8.2.1360: stray error for white space after expression

Problem:    Stray error for white space after expression.
Solution:   Ignore trailing white space. (closes #6608)
diff --git a/src/eval.c b/src/eval.c
index 119b7cc..87d2e16 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -300,7 +300,7 @@
 	s = skipwhite(s);
 	if (eval1_emsg(&s, rettv, NULL) == FAIL)
 	    return FAIL;
-	if (*s != NUL)  // check for trailing chars after expr
+	if (*skipwhite(s) != NUL)  // check for trailing chars after expr
 	{
 	    clear_tv(rettv);
 	    semsg(_(e_invexpr2), s);