patch 8.2.1430: Vim9: error for missing comma instead of extra white space

Problem:    Vim9: error for missing comma instead of extra white space.
Solution:   Check if comma can be found after white space. (closes #6668)
            Also check for extra white space in literal dict. (closes #6670)
diff --git a/src/dict.c b/src/dict.c
index b381d47..b6c9016 100644
--- a/src/dict.c
+++ b/src/dict.c
@@ -781,7 +781,7 @@
     tv->v_type = VAR_STRING;
     tv->vval.v_string = vim_strnsave(*arg, p - *arg);
 
-    *arg = skipwhite(p);
+    *arg = p;
     return OK;
 }
 
@@ -845,7 +845,12 @@
 	if (**arg != ':')
 	{
 	    if (evaluate)
-		semsg(_(e_missing_dict_colon), *arg);
+	    {
+		if (*skipwhite(*arg) == ':')
+		    semsg(_(e_no_white_before), ":");
+		else
+		    semsg(_(e_missing_dict_colon), *arg);
+	    }
 	    clear_tv(&tvkey);
 	    goto failret;
 	}