generator/generic-host: Handle missing configured platform

Sometimes, hosts don't have a platform configured in NetBox. This commit
handles this case properly by assuming those devices are not Linux
devices.

generate-icinga-generic-host.py

@@ -219,12 +219,13 @@ def create_icinga2_host_object_from_netbox(netbox, device_name):
                 continue
             ssh_ports.append(p)
 
-    device_platform = device.platform.slug
     device_is_linux = False
-    for linux_platform in LINUX_PLATFORMS:
-        if device_platform == linux_platform:
-            device_is_linux = True
-            break
+    if device.platform:
+        device_platform = device.platform.slug
+        for linux_platform in LINUX_PLATFORMS:
+            if device_platform == linux_platform:
+                device_is_linux = True
+                break
 
     if device_is_linux:
         host = Icinga2Host(