MOBILE-3384 login: Accept null in local_mobile check response

src/classes/site.ts

@@ -1376,6 +1376,11 @@ export class CoreSite {
             return { code: 0 };
         }
 
+        if (data === null) {
+            // This probably means that the server was configured to return null for non-existing URLs. Not installed.
+            return { code: 0 };
+        }
+
         if (typeof data != 'undefined' && data.errorcode === 'requirecorrectaccess') {
             if (!retrying) {
                 this.siteUrl = this.urlUtils.addOrRemoveWWW(this.siteUrl);

src/core/login/pages/site/site.ts

@@ -165,7 +165,14 @@ export class CoreLoginSitePage {
                     // Attempt guessing the domain if the initial check failed
                     const domain = CoreUrl.guessMoodleDomain(url);
 
-                    return domain ? this.sitesProvider.checkSite(domain) : Promise.reject(error);
+                    if (domain && domain != url) {
+                        return this.sitesProvider.checkSite(domain).catch((secondError) => {
+                            // Try to use the first error.
+                            return Promise.reject(error || secondError);
+                        });
+                    }
+
+                    return Promise.reject(error);
                 })
                 .then((result) => this.login(result))
                 .catch((error) => this.showLoginIssue(url, error))

src/providers/sites.ts

@@ -572,6 +572,11 @@ export class CoreSitesProvider {
             return Promise.reject({error: this.translate.instant('core.cannotconnect', {$a: CoreSite.MINIMUM_MOODLE_VERSION})});
         }).then((data: any) => {
 
+            if (data === null) {
+                // Cannot connect.
+                return Promise.reject({error: this.translate.instant('core.cannotconnect', {$a: CoreSite.MINIMUM_MOODLE_VERSION})});
+            }
+
             if (data.errorcode && (data.errorcode == 'enablewsdescription' || data.errorcode == 'requirecorrectaccess')) {
                 return Promise.reject({ errorcode: data.errorcode, error: data.error });
             } else if (data.error && data.error == 'Web services must be enabled in Advanced features.') {