fix: The provided Android NDK is vnull while the recommended one is v21.0.6113669 error in some cases

package.json

@@ -1,6 +1,6 @@
 {
   "name": "nativescript-dev-webpack",
-  "version": "1.5.0",
+  "version": "1.5.1",
   "main": "index",
   "description": "",
   "homepage": "http://www.telerik.com",
@@ -100,4 +100,4 @@
     "tns-core-modules": "next",
     "typescript": "~3.5.3"
   }
-}
+}

snapshot/android/snapshot-generator.js

@@ -400,7 +400,11 @@ SnapshotGenerator.prototype.buildCSource = function (androidArch, blobInputDir,
 }
 
 SnapshotGenerator.prototype.getRecommendedNdkWarning = function (localNdkRevision, recommendedAndroidNdkRevision) {
-    return `The provided Android NDK is v${localNdkRevision} while the recommended one is v${recommendedAndroidNdkRevision}`;
+    if (localNdkRevision) {
+        return `The provided Android NDK is v${localNdkRevision} while the required one is v${recommendedAndroidNdkRevision}`;
+    } else {
+        return `The provided Android NDK version is different than the required one - v${recommendedAndroidNdkRevision}`;
+    }
 }
 
 SnapshotGenerator.prototype.runMksnapshotTool = function (tool, mksnapshotParams, inputFile, snapshotInDocker, snapshotToolsPath, buildCSource) {