fix($compile): don't add leading white-space in attributes for a specific merge case

If the replaced element had an attribute with an empty ("") value, merging the attribute from
the template would result in a leading white-space.

Author: Narretz

src/ng/compile.js

@@ -2753,7 +2753,11 @@ function $CompileProvider($provide, $$sanitizeUriProvider) {
       forEach(dst, function(value, key) {
         if (key.charAt(0) !== '$') {
           if (src[key] && src[key] !== value) {
-            value += (key === 'style' ? ';' : ' ') + src[key];
+            if (value.length) {
+              value += (key === 'style' ? ';' : ' ') + src[key];
+            } else {
+              value = src[key];
+            }
           }
           dst.$set(key, value, true, srcAttr[key]);
         }

test/ng/compileSpec.js

@@ -980,6 +980,17 @@ describe('$compile', function() {
         }));
 
 
+        it('should not add white-space when merging an attribute that is "" in the replaced element',
+          inject(function($compile, $rootScope) {
+            element = $compile(
+              '<div><div replace class=""></div><div>')($rootScope);
+            var div = element.find('div');
+            expect(div.hasClass('log')).toBe(true);
+            expect(div.attr('class')).toBe('log');
+          })
+        );
+
+
         it('should not set merged attributes twice in $attrs', function() {
           var attrs;