MDEV-38642: Missing Null terminator in the definition of mysqldump's --system typelib

There was a missing NULL element terminator for --system's type
library definition.

This was causing a crash in find_type_eol when e.g. an incomplete
value was passed to --system where it keeps iterating until it
 finds the NULL as a typelib element.

Fixed by appending a NullS to the definition.
Test case added.

Author: gkodinov

client/mysqldump.c

@@ -138,10 +138,10 @@ static my_bool  verbose= 0, opt_no_create_info= 0, opt_no_data= 0, opt_no_data_m
 #define OPT_SYSTEM_STATS 32
 #define OPT_SYSTEM_TIMEZONES 64
 static const char *opt_system_type_values[]=
-  {"all", "users", "plugins",  "udfs", "servers", "stats", "timezones"};
+  {"all", "users", "plugins",  "udfs", "servers", "stats", "timezones", NullS};
 static TYPELIB opt_system_types=
 {
-  array_elements(opt_system_type_values), "system dump options",
+  array_elements(opt_system_type_values) - 1, "system dump options",
   opt_system_type_values, NULL
 };
 static ulonglong opt_system= 0ULL;

mysql-test/main/mysqldump-system-incomplete.result

@@ -0,0 +1,6 @@
+#
+# MDEV-38642 Missing Null terminator in the definition of mysqldump's
+#  --system typelib
+#
+# Should not crash
+# End of 10.6 tests

mysql-test/main/mysqldump-system-incomplete.test

@@ -0,0 +1,11 @@
+--source include/not_embedded.inc
+
+--echo #
+--echo # MDEV-38642 Missing Null terminator in the definition of mysqldump's
+--echo #  --system typelib
+--echo #
+
+--echo # Should not crash
+--exec $MYSQL_DUMP --system=user > /dev/null
+
+--echo # End of 10.6 tests