vim-patch:8.2.2515: memory access error when truncating an empty message

Problem:    Memory access error when truncating an empty message.
Solution:   Check for an empty string. (Dominique Pellé, closes vim/vim#7841)
6281815ecc

src/nvim/message.c

@@ -382,6 +382,13 @@ void trunc_string(char_u *s, char_u *buf, int room_in, int buflen)
   int i;
   int n;
 
+  if (*s == NUL) {
+    if (buflen > 0) {
+      *buf = NUL;
+    }
+    return;
+  }
+
   if (room_in < 3) {
     room = 0;
   }