[FIX] Application: Fallback to manifest.appdescr_variant if manifest.json is not found (#631)

This fixes a regression presumably present since ui5-project v3.0.0,
which prevented proper fallback to manifest.appdescr_variant in case no
manifest.json is found in the project.

Author: RandomByte

lib/specifications/types/Application.js

@@ -214,11 +214,16 @@ class Application extends ComponentProject {
 		return this._pManifests[filePath] = this._getRawSourceReader().byPath(filePath)
 			.then(async (resource) => {
 				if (!resource) {
-					throw new Error(
+					const error = new Error(
 						`Could not find resource ${filePath} in project ${this.getName()}`);
+					error.code = "ENOENT"; // "File or directory does not exist"
+					throw error;
 				}
 				return JSON.parse(await resource.getString());
 			}).catch((err) => {
+				if (err.code === "ENOENT") {
+					throw err;
+				}
 				throw new Error(
 					`Failed to read ${filePath} for project ` +
 					`${this.getName()}: ${err.message}`);

test/lib/specifications/types/Application.js

@@ -583,10 +583,10 @@ test.serial("_getManifest: File does not exist", async (t) => {
 	const project = await Specification.create(projectInput);
 
 	const error = await t.throwsAsync(project._getManifest("/does-not-exist.json"));
-	t.deepEqual(error.message,
-		"Failed to read /does-not-exist.json for project application.a: " +
+	t.is(error.message,
 		"Could not find resource /does-not-exist.json in project application.a",
 		"Rejected with correct error message");
+	t.is(error.code, "ENOENT");
 });
 
 test.serial("_getManifest: result is cached", async (t) => {