patch 8.2.1945: crash when passing NULL function to reduce()

Problem:    Crash when passing NULL function to reduce().
Solution:   Check for NULL pointer and give an error. (Dominique Pellé,
            closes #7243)
diff --git a/src/version.c b/src/version.c
index 714d038..8052de8 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1945,
+/**/
     1944,
 /**/
     1943,