fix(copy): clear array destinations correctly for non-array sources

Closes #8610
Closes #8702

Author: caitp

src/Angular.js

@@ -800,9 +800,13 @@ function copy(source, destination, stackSource, stackDest) {
       }
     } else {
       var h = destination.$$hashKey;
-      forEach(destination, function(value, key) {
-        delete destination[key];
-      });
+      if (isArray(destination)) {
+        destination.length = 0;
+      } else {
+        forEach(destination, function(value, key) {
+          delete destination[key];
+        });
+      }
       for ( var key in source) {
         if(source.hasOwnProperty(key)) {
           result = copy(source[key], null, stackSource, stackDest);

test/AngularSpec.js

@@ -184,6 +184,12 @@ describe('angular', function() {
       expect(aCopy).toBe(aCopy.self);
       expect(aCopy.selfs[2]).not.toBe(a.selfs[2]);
     });
+
+    it('should clear destination arrays correctly when source is non-array', function() {
+      expect(copy(null, [1,2,3])).toEqual([]);
+      expect(copy(undefined, [1,2,3])).toEqual([]);
+      expect(copy({0: 1, 1: 2}, [1,2,3])).toEqual([1,2]);
+    });
   });
 
   describe("extend", function() {