[5.x] Throw exception when minProcesses is set to zero (#988)

* throw exception when minProcesses is set to zero

* Update ProvisioningPlan.php

Co-authored-by: Taylor Otwell <taylor@laravel.com>

src/ProvisioningPlan.php

@@ -2,6 +2,7 @@
 
 namespace Laravel\Horizon;
 
+use Exception;
 use Illuminate\Support\Arr;
 use Illuminate\Support\Str;
 use Laravel\Horizon\Contracts\HorizonCommandQueue;
@@ -177,6 +178,10 @@ protected function convert($supervisor, $options)
             return [Str::camel($key) => $value];
         })->all();
 
+        if (isset($options['minProcesses']) && $options['minProcesses'] === 0) {
+            throw new Exception("The value of [{$supervisor}.minProcesses] must be greater than 0.");
+        }
+
         $options['parentId'] = getmypid();
 
         return SupervisorOptions::fromArray(