fix: heatmap fails when no hosts defined.

* we should just display the page with no data instead of app error when
  during new installs someone runs --regen-heatmap.

Change-Id: I61116b1cc7e27617bab7e59500eb3d8097ab1a1e

src/quads/tools/simple_table_generator.py

@@ -167,8 +167,12 @@ async def generator(self, _host_file, _days, _month, _year, _gentime):
 
         total_hosts = len(hosts)
         total_use = len(total_current_schedules)
-        utilization = 100 - (non_allocated_count * 100 // (_days * total_hosts))
-        utilization_daily = total_use * 100 // total_hosts
+        if int(total_hosts) == 0:
+            utilization_daily = 0
+            utilization = 0
+        else:
+            utilization = 100 - (non_allocated_count * 100 // (_days * total_hosts))
+            utilization_daily = total_use * 100 // total_hosts
         with open(os.path.join(Config.TEMPLATES_PATH, "simple_table_emoji")) as _file:
             template = Template(_file.read())
         content = template.render(