patch 8.2.1324: Vim9: line break after "=" does not work

Problem:    Vim9: line break after "=" does not work.
Solution:   Also allow for NUL after "=". (closes #6549)
diff --git a/src/evalvars.c b/src/evalvars.c
index f409f8c..73c4da6 100644
--- a/src/evalvars.c
+++ b/src/evalvars.c
@@ -801,13 +801,13 @@
 	    else
 		++expr;
 
-	    if (vim9script && (!VIM_ISWHITE(*argend) || !VIM_ISWHITE(*expr)))
+	    if (vim9script && (!VIM_ISWHITE(*argend)
+						   || !IS_WHITE_OR_NUL(*expr)))
 	    {
 		vim_strncpy(op, expr - len, len);
 		semsg(_(e_white_both), op);
 		i = FAIL;
 	    }
-	    expr = skipwhite(expr);
 
 	    if (eap->skip)
 		++emsg_skip;
@@ -818,6 +818,7 @@
 		evalarg.eval_getline = eap->getline;
 		evalarg.eval_cookie = eap->cookie;
 	    }
+	    expr = skipwhite_and_linebreak(expr, &evalarg);
 	    i = eval0(expr, &rettv, eap, &evalarg);
 	    if (eap->skip)
 		--emsg_skip;