[js] Couple of additional checks for module existence

lib/modules/database/index.js

@@ -211,7 +211,7 @@ export default class Database extends Base {
 }
 
 export const statics = {
-  ServerValue: {
+  ServerValue: FirebaseDatabase ? {
     TIMESTAMP: FirebaseDatabase.serverValueTimestamp || { '.sv': 'timestamp' },
-  },
+  } : {},
 };

lib/modules/storage/index.js

@@ -148,7 +148,7 @@ export const statics = {
     CANCELLED: 'cancelled',
     ERROR: 'error',
   },
-  Native: {
+  Native: FirebaseStorage ? {
     MAIN_BUNDLE_PATH: FirebaseStorage.MAIN_BUNDLE_PATH,
     CACHES_DIRECTORY_PATH: FirebaseStorage.CACHES_DIRECTORY_PATH,
     DOCUMENT_DIRECTORY_PATH: FirebaseStorage.DOCUMENT_DIRECTORY_PATH,
@@ -158,5 +158,5 @@ export const statics = {
     LIBRARY_DIRECTORY_PATH: FirebaseStorage.LIBRARY_DIRECTORY_PATH,
     FILETYPE_REGULAR: FirebaseStorage.FILETYPE_REGULAR,
     FILETYPE_DIRECTORY: FirebaseStorage.FILETYPE_DIRECTORY,
-  },
+  } : {},
 };