Fixed intermittent crashes in fullscreen zooming

[kevwkev]

When zooming in and out multiple times quickly on an image in
fullscreen mode, the example application crashes intermittently.
stops at line:
"for (UIPhotoContainerView *subView in reusableViews) {" from
"UIPhotoGalleryView.m"

breakpoint analyzer:
#0 0x38dd9cc0 in objc_exception_throw ()
#1 0x2e4c99f0 in __NSFastEnumerationMutationHandler ()
#2 0x0009d61c in -[UIPhotoGalleryView scrollViewDidScroll:] at

UIPhotoGallery/UIPhotoGalleryView.m:172
#3 0x311026e4 in -UIScrollView(UIScrollViewInternal) _notifyDidScroll

[mickey35vn]

It isn't good solution. To fix this issue, we just change the calculate of new page

int nextPage = (NSInteger)ceilf(newPage);
if (newPage > (float)currentPage) // next page
{
nextPage = (NSInteger)floorf(newPage);
}
if (nextPage != currentPage) {
currentPage = nextPage;
for (UIPhotoContainerView *subView in reusableViews) {
if (subView.tag != newPage) {
[subView resetZoom];
}
}

    [self populateSubviews];
}