patch 9.0.0684: skipped :exe command fails compilation on MS-Windows

Problem:    Skipped :exe command fails compilation on MS-Windows.
Solution:   Adjust return value when skipping.
diff --git a/src/vim9instr.c b/src/vim9instr.c
index 4407d59..9c3b2a9 100644
--- a/src/vim9instr.c
+++ b/src/vim9instr.c
@@ -1876,6 +1876,7 @@
 {
     isn_T	*isn;
 
+    RETURN_OK_IF_SKIP(cctx);
     if ((isn = generate_instr_drop(cctx, isn_type, count)) == NULL)
 	return FAIL;
     isn->isn_arg.number = count;