patch 8.2.1899: crash in out-of-memory situation

Problem:    Crash in out-of-memory situation.
Solution:   Bail out if shell_name is NULL. (Dominique Pellé, closes #7196)

src/ex_cmds.c

@@ -1544,6 +1544,9 @@ make_filter_cmd(
     int		is_fish_shell;
     char_u	*shell_name = get_isolated_shell_name();
 
+    if (shell_name == NULL)
+	return NULL;
+
     // Account for fish's different syntax for subshells
     is_fish_shell = (fnamecmp(shell_name, "fish") == 0);
     vim_free(shell_name);

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1899,
 /**/
     1898,
 /**/