patch 8.0.0074
Problem:    Cannot make Vim fail on an internal error.
Solution:   Add IEMSG() and IEMSG2(). (Domenique Pelle)  Avoid reporting an
            internal error without mentioning where.
diff --git a/src/memfile.c b/src/memfile.c
index 2f75201..0fb2787 100644
--- a/src/memfile.c
+++ b/src/memfile.c
@@ -482,7 +482,7 @@
     flags = hp->bh_flags;
 
     if ((flags & BH_LOCKED) == 0)
-	EMSG(_("E293: block was not locked"));
+	IEMSG(_("E293: block was not locked"));
     flags &= ~BH_LOCKED;
     if (dirty)
     {