iOS: Handle portrait image that doesn't fill message box

It would have rounded corners inside of the bubble, which is not what
we want. This makes the bubble itself have the rounded corners, and then
it cuts off anything that would extend past its edges.

stylesheets/_ios.scss

@@ -234,6 +234,7 @@ $ios-border-color: rgba(0,0,0,0.1);
   .inner-bubble {
     border-radius: 15px;
     margin-bottom: 5px;
+    overflow: hidden;
 
     .body {
       margin-top: 0;
@@ -242,10 +243,6 @@ $ios-border-color: rgba(0,0,0,0.1);
       position: relative;
       word-break: break-word;
     }
-
-    .attachments img {
-      border-radius: 15px;
-    }
   }
 
   .inner-bubble.with-tail {