patch 8.2.4552: in a :def function "put = expr" does not work

Problem:    In a :def function "put = expr" does not work.
Solution:   Skip over white space. (closes #9936)
diff --git a/src/vim9cmds.c b/src/vim9cmds.c
index 5a44644..b8a511f 100644
--- a/src/vim9cmds.c
+++ b/src/vim9cmds.c
@@ -1767,7 +1767,7 @@
 
     if (eap->regname == '=')
     {
-	char_u *p = line + 1;
+	char_u *p = skipwhite(line + 1);
 
 	if (compile_expr0(&p, cctx) == FAIL)
 	    return NULL;