patch 8.2.1800: Vim9: memory leak if "if" condition is invalid

Problem:    Vim9: memory leak if "if" condition is invalid.
Solution:   Free ppconst earlier.
diff --git a/src/vim9compile.c b/src/vim9compile.c
index 8d362ab..373d76c 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -5721,10 +5721,10 @@
 
 	// The expression results in a constant.
 	v = tv_get_bool_chk(&ppconst.pp_tv[0], &error);
+	clear_ppconst(&ppconst);
 	if (error)
 	    return NULL;
 	cctx->ctx_skip = v ? SKIP_NOT : SKIP_YES;
-	clear_ppconst(&ppconst);
     }
     else
     {