avoid build failure when gradle.properties file is missing

Author: maxme

WordPressUtils/build.gradle

@@ -36,7 +36,11 @@ android {
 uploadArchives {
     repositories {
         mavenDeployer {
-            repository(url: project.repository)
+            def repo_url = ""
+            if (project.hasProperty("repository")) {
+                repo_url = project.repository
+            }
+            repository(url: repo_url)
             pom.version = android.defaultConfig.versionName
             pom.groupId = "org.wordpress"
             pom.artifactId = "wordpress-utils"