Only draw weather chart when forecast is present (#239)

* Only draw weather chart when forecast is present

* Update ha-weather-card.html

* Update ha-weather-card.html

src/cards/ha-weather-card.html

@@ -21,7 +21,7 @@
     <google-legacy-loader on-api-load='googleApiLoaded'></google-legacy-loader>
     <ha-card header='[[computeTitle(stateObj)]]'>
       <div class='content'>
-        <div id='chart_id'></div>
+        <div id='chart_id' hidden$="[[!stateObj.attributes.forecast]]"></div>
         <ha-attributes state-obj='[[stateObj]]' extra-filters='forecast'></ha-attributes>
       </div>
     </ha-card>
@@ -83,6 +83,10 @@
           this.$.chart_id);
       }
 
+      if (!this.stateObj.attributes || !this.stateObj.attributes.forecast) {
+        return;
+      }
+
       this.drawChart();
     },