Tweak user agent building to avoid multiple spaces

Bug: 3211038
 The building of the user agent could previously have multiple sequential
 spaces. This was causing the CTS test to fail.

Change-Id: I13fc76ba6b97ee84dd44461b4d03b6ca70b48cdf

core/java/android/webkit/WebSettings.java

@@ -485,11 +485,12 @@ public class WebSettings {
             // default to "en"
             buffer.append("en");
         }
-        buffer.append("; ");
+        buffer.append(";");
         // add the model for the release build
         if ("REL".equals(Build.VERSION.CODENAME)) {
             final String model = Build.MODEL;
             if (model.length() > 0) {
+                buffer.append(" ");
                 buffer.append(model);
             }
         }