Merge pull request #4708 from NativeScript/fatme/fix-source-of-undefined

fix: fix cannot read property sourceMap of undefined

Author: Fatme

lib/services/webpack/webpack-compiler-service.ts

@@ -138,7 +138,7 @@ export class WebpackCompilerService extends EventEmitter implements IWebpackComp
 
 		envData.verbose = this.$logger.isVerbose();
 		envData.production = prepareData.release;
-		if (prepareData.env.sourceMap === false || prepareData.env.sourceMap === 'false') {
+		if (prepareData.env && (prepareData.env.sourceMap === false || prepareData.env.sourceMap === 'false')) {
 			delete envData.sourceMap;
 		} else if (!prepareData.release) {
 			envData.sourceMap = true;