Fatal error: Call to undefined method stdClass::getType() in generate.make.inc (D7)

When running `drush generate-makefile` on a D7 site, the command fails with a fatal error, when there are any custom projects. This is due to the changes in #904, as that was only "fixed" for D8 there.

```
PHP Fatal error:  Call to undefined method stdClass::getType() in /Users/derhasi/.composer/vendor/drush/drush/commands/make/generate.make.inc on line 167
PHP Stack trace:
PHP   1. {main}() /Users/derhasi/.composer/vendor/drush/drush/drush.php:0
PHP   2. drush_main() /Users/derhasi/.composer/vendor/drush/drush/drush.php:16
PHP   3. Drush\Boot\DrupalBoot->bootstrap_and_dispatch() /Users/derhasi/.composer/vendor/drush/drush/drush.php:76
PHP   4. drush_dispatch() /Users/derhasi/.composer/vendor/drush/drush/lib/Drush/Boot/DrupalBoot.php:46
PHP   5. call_user_func_array:{/Users/derhasi/.composer/vendor/drush/drush/includes/command.inc:178}() /Users/derhasi/.composer/vendor/drush/drush/includes/command.inc:178
PHP   6. drush_command() /Users/derhasi/.composer/vendor/drush/drush/includes/command.inc:178
PHP   7. _drush_invoke_hooks() /Users/derhasi/.composer/vendor/drush/drush/includes/command.inc:210
PHP   8. call_user_func_array:{/Users/derhasi/.composer/vendor/drush/drush/includes/command.inc:359}() /Users/derhasi/.composer/vendor/drush/drush/includes/command.inc:359
PHP   9. drush_make_generate() /Users/derhasi/.composer/vendor/drush/drush/includes/command.inc:359
PHP  10. _drush_make_generate_projects() /Users/derhasi/.composer/vendor/drush/drush/commands/make/generate.make.inc:17
PHP  11. _drush_generate_custom_project() /Users/derhasi/.composer/vendor/drush/drush/commands/make/generate.make.inc:128

Fatal error: Call to undefined method stdClass::getType() in /Users/derhasi/.composer/vendor/drush/drush/commands/make/generate.make.inc on line 167

Call Stack:
    0.0008     233224   1. {main}() /Users/derhasi/.composer/vendor/drush/drush/drush.php:0
    0.0289     302952   2. drush_main() /Users/derhasi/.composer/vendor/drush/drush/drush.php:16
    0.1881    2547184   3. Drush\Boot\DrupalBoot->bootstrap_and_dispatch() /Users/derhasi/.composer/vendor/drush/drush/drush.php:76
    0.7141    7775544   4. drush_dispatch() /Users/derhasi/.composer/vendor/drush/drush/lib/Drush/Boot/DrupalBoot.php:46
    0.9635   11093104   5. call_user_func_array:{/Users/derhasi/.composer/vendor/drush/drush/includes/command.inc:178}() /Users/derhasi/.composer/vendor/drush/drush/includes/command.inc:178
    0.9635   11093440   6. drush_command() /Users/derhasi/.composer/vendor/drush/drush/includes/command.inc:178
    0.9638   11094240   7. _drush_invoke_hooks() /Users/derhasi/.composer/vendor/drush/drush/includes/command.inc:210
    0.9736   11163944   8. call_user_func_array:{/Users/derhasi/.composer/vendor/drush/drush/includes/command.inc:359}() /Users/derhasi/.composer/vendor/drush/drush/includes/command.inc:359
    0.9736   11164280   9. drush_make_generate() /Users/derhasi/.composer/vendor/drush/drush/includes/command.inc:359
    1.4336   12952248  10. _drush_make_generate_projects() /Users/derhasi/.composer/vendor/drush/drush/commands/make/generate.make.inc:17
   31.6883   19086648  11. _drush_generate_custom_project() /Users/derhasi/.composer/vendor/drush/drush/commands/make/generate.make.inc:128

Drush command terminated abnormally due to an unrecoverable error.                                                                                 [error]
Error: Call to undefined method stdClass::getType() in /Users/derhasi/.composer/vendor/drush/drush/commands/make/generate.make.inc, line 167
```