fix($rootScope): don't clear phase if $apply is re-entered

We cannot re-enter a `$apply` block while already in a `$apply` or `$digest`
phase.

Before this change such an invalid call to `$apply` was incorrectly clearing
the phase, which meant that a second invalid `$apply` call was being allowed.

Closes angular#12174

Author: lgalfaso

src/ng/rootScope.js

@@ -1040,11 +1040,14 @@ function $RootScopeProvider() {
       $apply: function(expr) {
         try {
           beginPhase('$apply');
-          return this.$eval(expr);
+          try {
+            return this.$eval(expr);
+          } finally {
+            clearPhase();
+          }
         } catch (e) {
           $exceptionHandler(e);
         } finally {
-          clearPhase();
           try {
             $rootScope.$digest();
           } catch (e) {

test/ng/rootScopeSpec.js

@@ -1505,6 +1505,22 @@ describe('Scope', function() {
       }));
 
 
+      it('should not clear the state when calling $apply during an $apply', inject(
+          function($rootScope) {
+        $rootScope.$apply(function() {
+          expect(function() {
+            $rootScope.$apply();
+          }).toThrowMinErr('$rootScope', 'inprog', '$apply already in progress');
+          expect(function() {
+            $rootScope.$apply();
+          }).toThrowMinErr('$rootScope', 'inprog', '$apply already in progress');
+        });
+        expect(function() {
+          $rootScope.$apply();
+        }).not.toThrow();
+      }));
+
+
       it('should throw an exception if $apply is called while flushing evalAsync queue', inject(
           function($rootScope) {
         expect(function() {