patch 8.2.4296: Vim9: not all code covered by tests

Problem:    Vim9: not all code covered by tests.
Solution:   Add a few more tests for corner cases.  Fix hang when single quote
            is missing.
diff --git a/src/vim9expr.c b/src/vim9expr.c
index d36df84..146e136 100644
--- a/src/vim9expr.c
+++ b/src/vim9expr.c
@@ -2824,8 +2824,10 @@
     // Ignore all kinds of errors when not producing code.
     if (cctx->ctx_skip == SKIP_YES)
     {
+	int		prev_did_emsg = did_emsg;
+
 	skip_expr_cctx(arg, cctx);
-	return OK;
+	return did_emsg == prev_did_emsg ? OK : FAIL;
     }
 
     // Evaluate the first expression.