fix(modal): correctly close modals with no backdrop

backdropDomEl was not initialised if only modal without backdrop was opened.

Closes #974
Closes #979

src/modal/modal.js

@@ -136,7 +136,7 @@ angular.module('ui.bootstrap.modal', [])
         modalWindow.modalDomEl.remove();
 
         //remove backdrop if no longer needed
-        if (backdropIndex() == -1) {
+        if (backdropDomEl && backdropIndex() == -1) {
           backdropDomEl.remove();
           backdropDomEl = undefined;
         }
@@ -312,4 +312,4 @@ angular.module('ui.bootstrap.modal', [])
     };
 
     return $modalProvider;
-  });
+  });

src/modal/test/modal.spec.js

@@ -351,12 +351,15 @@ describe('$modal', function () {
     describe('backdrop', function () {
 
       it('should not have any backdrop element if backdrop set to false', function () {
-        open({
+        var modal =open({
           template: '<div>No backdrop</div>',
           backdrop: false
         });
         expect($document).toHaveModalOpenWithContent('No backdrop', 'div');
         expect($document).not.toHaveBackdrop();
+
+        dismiss(modal);
+        expect($document).toHaveModalsOpen(0);
       });
 
       it('should not close modal on backdrop click if backdrop is specified as "static"', function () {