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)

Author: brammool

src/errors.h

@@ -286,4 +286,6 @@ EXTERN char e_cannot_add_to_null_list[]
 	INIT(= N_("E1130: Cannot add to null list"));
 EXTERN char e_cannot_add_to_null_blob[]
 	INIT(= N_("E1131: Cannot add to null blob"));
+EXTERN char e_missing_function_argument[]
+	INIT(= N_("E1132: Missing function argument"));
 #endif

src/list.c

@@ -2552,8 +2552,11 @@ f_reduce(typval_T *argvars, typval_T *rettv)
     }
     else
 	func_name = tv_get_string(&argvars[1]);
-    if (*func_name == NUL)
-	return;		// type error or empty name
+    if (func_name == NULL || *func_name == NUL)
+    {
+	emsg(_(e_missing_function_argument));
+	return;
+    }
 
     vim_memset(&funcexe, 0, sizeof(funcexe));
     funcexe.evaluate = TRUE;

src/testdir/test_listdict.vim

@@ -740,6 +740,9 @@ func Test_reduce()
 
   call assert_equal(42, reduce(test_null_list(), function('add'), 42))
   call assert_equal(42, reduce(test_null_blob(), function('add'), 42))
+
+  " should not crash
+  call assert_fails('echo reduce([1], test_null_function())', 'E1132:')
 endfunc
 
 " splitting a string to a List using split()

src/version.c

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