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)

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1945,
 /**/
     1944,
 /**/