clients/android: handle missing keystore.properties in docker-based build

Signed-off-by: Sebastien Binet <binet@cern.ch>

clients/android/build-in-docker.go

@@ -65,8 +65,22 @@ func buildApp() {
 	}
 	cmd.Stdout = os.Stdout
 	cmd.Stderr = os.Stderr
-	if err := cmd.Run(); err != nil {
-		log.Fatalf("Error building Android app: %v", err)
+
+	if _, err := os.ReadFile("./keystore.properties"); err != nil {
+		// no keystore.
+		// generate one that's in line with the one from devenv/Dockerfile.
+
+		const keystore = `## Code generated by perkeep; DO NOT EDIT.
+storeFile=/home/gopher/keystore
+storePassword=gopher
+keyAlias=perkeep
+keyPassword=gopher
+`
+		err = os.WriteFile("./keystore.properties", []byte(keystore), 0644)
+		if err != nil {
+			log.Fatalf("could not write default keystore.properties: %+v", err)
+		}
+		defer os.Remove("./keystore.properties")
 	}
 }