Clean up thumbnail-related logic.

Signal/src/ViewControllers/MediaDetailViewController.m

@@ -79,6 +79,7 @@ NS_ASSUME_NONNULL_BEGIN
         thumbnailImageLargeWithSuccess:^(UIImage *image) {
             weakSelf.image = image;
             [weakSelf createContents];
+            [weakSelf updateMinZoomScale];
         }
         failure:^{
             DDLogWarn(@"Could not load media.");
@@ -127,6 +128,13 @@ NS_ASSUME_NONNULL_BEGIN
 
 - (void)updateMinZoomScale
 {
+    if (!self.image) {
+        self.scrollView.minimumZoomScale = 1.f;
+        self.scrollView.maximumZoomScale = 1.f;
+        self.scrollView.zoomScale = 1.f;
+        return;
+    }
+
     CGSize viewSize = self.scrollView.bounds.size;
     UIImage *image = self.image;
     OWSAssert(image);

SignalServiceKit/src/Messages/Attachments/OWSThumbnailService.swift

@@ -146,6 +146,9 @@ private struct OWSThumbnailRequest {
             }
             return OWSLoadedThumbnail(image: image, filePath: thumbnailPath)
         }
+
+        Logger.verbose("Creating thumbnail of size: \(thumbnailRequest.thumbnailDimensionPoints)")
+
         let thumbnailDirPath = (thumbnailPath as NSString).deletingLastPathComponent
         guard OWSFileSystem.ensureDirectoryExists(thumbnailDirPath) else {
             throw OWSThumbnailError.failure(description: "Could not create attachment's thumbnail directory.")

SignalServiceKit/src/Messages/Attachments/TSAttachmentStream.m

@@ -20,7 +20,7 @@ const NSUInteger ThumbnailDimensionPointsLarge()
 {
     CGSize screenSizePoints = UIScreen.mainScreen.bounds.size;
     const CGFloat kMinZoomFactor = 2.f;
-    return MAX(screenSizePoints.width * kMinZoomFactor, screenSizePoints.height * kMinZoomFactor);
+    return MAX(screenSizePoints.width, screenSizePoints.height) * kMinZoomFactor;
 }
 
 typedef void (^OWSLoadedThumbnailSuccess)(OWSLoadedThumbnail *loadedThumbnail);