Platform.identify fails if no match for platform and no default

Fix adds check if default option is present. It runs default
function if provided or returns undefined.

Author: dgolovin

browser/services/platform.js

@@ -5,7 +5,8 @@ class Platform {
     try {
       return map[Platform.OS]();
     } catch (error) {
-      return map['default']();
+      let defaultCallback = map['default'];
+      return defaultCallback ? defaultCallback() : undefined;
     }
   }
 

test/unit/services/platform-test.js

@@ -24,6 +24,11 @@ describe('Platform', function(){
       linux: ()=>'linux',
       default: ()=>'bummer'
     };
+    let noDefaultData = {
+      darwin: ()=>'darwin',
+      win32: ()=>'win32',
+      linux: ()=>'linux'
+    };
 
     it('returns value of opject\'s property named the same as current platform', function(){
       sandbox.stub(Platform,'getOS').returns('win32');
@@ -39,6 +44,11 @@ describe('Platform', function(){
       expect(Platform.identify(data)).to.be.equal('bummer');
     });
 
+    it('returns undefined if there no propyrty with current platform name and no default provided', function(){
+      sandbox.stub(Platform,'getOS').returns('ps/2');
+      expect(Platform.identify(noDefaultData)).to.be.equal(undefined);
+    });
+
   });
 
   describe('PATH', function(){