iOS: fixed #779 (selected text glitch)

Easier than expected; just needed to detect when it's been blanked and
force a redraw.  Makes loading a different story tidier, too.

clients/ios/Classes/StoryDetailViewController.m

@@ -205,6 +205,7 @@
 
 - (void)viewDidDisappear:(BOOL)animated {
     [super viewDidDisappear:animated];
+    [self clearStory];
 }
 
 - (void)viewWillDisappear:(BOOL)animated {
@@ -226,6 +227,10 @@
         _orientation = [UIApplication sharedApplication].statusBarOrientation;
         NSLog(@"Found stale orientation in story detail: %@", NSStringFromCGSize(self.view.bounds.size));
     }
+    
+    if ([self.webView.request.URL.absoluteString isEqualToString:@"about:blank"]) {
+        [self drawStory];
+    }
 }
 
 - (void)viewDidAppear:(BOOL)animated {