patch 8.2.1328: no space allowed before comma in list

Problem:    No space allowed before comma in list.
Solution:   Legacy Vim script allows it. (closes #6577)
diff --git a/src/dict.c b/src/dict.c
index 019227f..af1e1e9 100644
--- a/src/dict.c
+++ b/src/dict.c
@@ -838,7 +838,7 @@
 		: eval1(arg, &tvkey, evalarg)) == FAIL)	// recursive!
 	    goto failret;
 
-	// The colon should come right after the key, but this wasn't checked
+	// the colon should come right after the key, but this wasn't checked
 	// previously, so only require it in Vim9 script.
 	if (!vim9script)
 	    *arg = skipwhite(*arg);
@@ -895,7 +895,10 @@
 	}
 	clear_tv(&tvkey);
 
-	// the comma must come after the value
+	// the comma should come right after the value, but this wasn't checked
+	// previously, so only require it in Vim9 script.
+	if (!vim9script)
+	    *arg = skipwhite(*arg);
 	had_comma = **arg == ',';
 	if (had_comma)
 	{