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 #7841)
diff --git a/src/version.c b/src/version.c
index 21316e2..f856d83 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2515,
+/**/
     2514,
 /**/
     2513,