fix(plugin): handle rejection when Cordova is undefined

Zone.js now (helpfully) throws an error on unhandled rejections in
promises. This is great because they no longer silently fail, but we
were relying on that behavior for the case where the plugin isn't
installed or Cordova isn't available. With this change, those cases
won't throw an unhandled rejection error, but all regular plugin errors
still should.

src/plugins/plugin.ts

@@ -81,17 +81,15 @@ function callCordovaPlugin(pluginObj:any, methodName:string, args:any[], opts:an
     // Do this check in here in the case that the Web API for this plugin is available (for example, Geolocation).
     if(!window.cordova) {
       cordovaWarn(pluginObj.name, methodName);
-      reject && reject({
+      return {
         error: 'cordova_not_available'
-      });
-      return;
+      }
     }
 
     pluginWarn(pluginObj, methodName);
-    reject && reject({
+    return {
       error: 'plugin_not_installed'
-    });
-    return;
+    };
   }
 
   // console.log('Cordova calling', pluginObj.name, methodName, args);
@@ -118,14 +116,27 @@ function getPromise(cb) {
 }
 
 function wrapPromise(pluginObj:any, methodName:string, args:any[], opts:any={}) {
-  return getPromise((resolve, reject) => {
-    callCordovaPlugin(pluginObj, methodName, args, opts, resolve, reject);
-  })
+  let pluginResult, rej;
+  const p = getPromise((resolve, reject) => {
+    pluginResult = callCordovaPlugin(pluginObj, methodName, args, opts, resolve, reject);
+    rej = reject;
+  });
+  // Angular throws an error on unhandled rejection, but in this case we have already printed
+  // a warning that Cordova is undefined or the plugin is uninstalled, so there is no reason
+  // to error
+  if (pluginResult && pluginResult.error) {
+    p.catch(() => {});
+    rej(pluginResult.error);
+  }
+  return p;
 }
 
 function wrapObservable(pluginObj:any, methodName:string, args:any[], opts:any = {}) {
   return new Observable(observer => {
     let pluginResult = callCordovaPlugin(pluginObj, methodName, args, opts, observer.next.bind(observer), observer.error.bind(observer));
+    if (pluginResult && pluginResult.error) {
+      observer.error(pluginResult.error);
+    }
 
     return () => {
       try {