make debug app building easier

app/build.gradle

@@ -4,7 +4,9 @@ apply plugin: 'kotlin-android-extensions'
 
 def keystorePropertiesFile = rootProject.file("keystore.properties")
 def keystoreProperties = new Properties()
+if (keystorePropertiesFile.exists()) {
     keystoreProperties.load(new FileInputStream(keystorePropertiesFile))
+}
 
 android {
     compileSdkVersion 28
@@ -22,6 +24,7 @@ android {
     }
 
     signingConfigs {
+        if (keystorePropertiesFile.exists()) {
             release {
                 keyAlias keystoreProperties['keyAlias']
                 keyPassword keystoreProperties['keyPassword']
@@ -29,6 +32,7 @@ android {
                 storePassword keystoreProperties['storePassword']
             }
         }
+    }
 
     buildTypes {
         debug {