Fix issue causing blank white dialog when loading friends list

Summary:
Set the UIActivityIndicator color to gray to stop it from blending into the background.
On iOS5 we do this by setting the color to gray. On older iOS versions which don't support this
property, this is done by setting the style to UIActivityIndicatorViewStyleGray instead of
UIActivityIndicatorViewStyleWhiteLarge which results in a slightly smaller indicator.

Test Plan: Testing using Hackbook.

Reviewers: jacl, dgibson

Reviewed By: jacl

Differential Revision: https://phabricator.fb.com/D426894

Task ID: 908016

src/FBDialog.m

@@ -367,6 +367,11 @@ - (id)init {
 
         _spinner = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:
                     UIActivityIndicatorViewStyleWhiteLarge];
+        if ([_spinner respondsToSelector:@selector(setColor:)]) {
+            [_spinner setColor:[UIColor grayColor]];
+        } else {
+            [_spinner setActivityIndicatorViewStyle:UIActivityIndicatorViewStyleGray];
+        }
         _spinner.autoresizingMask =
         UIViewAutoresizingFlexibleTopMargin | UIViewAutoresizingFlexibleBottomMargin
         | UIViewAutoresizingFlexibleLeftMargin | UIViewAutoresizingFlexibleRightMargin;