Fix cocoa plugin build with OS X 10.8 SDK

With the 10.8 SDK, NSArray may not respond to firstObject which ends the
build with an error. This implementation doesn't use it and also handles
the case where no screen is available when calling
qt_mac_mainScreenHeight

Change-Id: Idce278423c37cc24d8fc31062a386e78d6487492
Reviewed-by: Jake Petroules <jake.petroules@theqtcompany.com>

1 files changed, 8 insertions, 4 deletions

diff --git a/src/plugins/platforms/cocoa/qcocoahelpers.mm b/src/plugins/platforms/cocoa/qcocoahelpers.mm
index 8ad80333f8..f51c21ee9b 100644
--- a/src/plugins/platforms/cocoa/qcocoahelpers.mm
+++ b/src/plugins/platforms/cocoa/qcocoahelpers.mm
@@ -634,10 +634,14 @@ QString qt_mac_applicationName()
 int qt_mac_mainScreenHeight()
 {
     QMacAutoReleasePool pool;
-    // The first screen in the screens array is documented
-    // to have the (0,0) origin.
-    NSRect screenFrame = [[[NSScreen screens] firstObject] frame];
-    return screenFrame.size.height;
+    NSArray *screens = [NSScreen screens];
+    if ([screens count] > 0) {
+        // The first screen in the screens array is documented
+        // to have the (0,0) origin.
+        NSRect screenFrame = [[screens objectAtIndex: 0] frame];
+        return screenFrame.size.height;
+    }
+    return 0;
 }
 
 int qt_mac_flipYCoordinate(int y)