Fix memory leak: return early on image cache hit in MessageImageView (#93)

The .task block checked NSCache on cache hit but never returned, causing
getMediaContent to be called on every channel visit even for already-cached
images.

The fix always fetches raw data via the SDK (which hits its own disk cache
on repeat loads, avoiding network requests), then skips the expensive decode
step (toOrientedImage) when the NSImage is already in the NSCache.

Two caching layers serve different purposes:
- NSCache (checked in init): synchronously pre-populates `image` before the
  view appears, preventing flicker on scroll/revisit. The image is already
  on screen before .task runs its disk read.
- SDK media cache (getMediaContent): avoids network re-fetches. Always
  called so `imageData` is populated for drag-and-drop, regardless of
  whether the decoded NSImage is cached.

Fixes #89

Author: beezly

Mactrix/Views/ChatView/MessageImageView.swift

@@ -93,14 +93,23 @@ struct MessageImageView: View {
                 return
             }
 
-            let cacheKey = NSString(string: content.source.url())
-            if let cached = MatrixClient.imageCache.object(forKey: cacheKey) {
-                image = Image(nsImage: cached)
-            }
-
+            // Two caching layers serve different purposes:
+            // - NSCache (checked in init): synchronously pre-populates `image` before the
+            //   view appears, preventing flicker on scroll/revisit. Also skips the expensive
+            //   decode step (toOrientedImage) on repeat loads below.
+            // - SDK media cache (getMediaContent): avoids network re-fetches. Always called
+            //   here so `imageData` is populated for drag-and-drop, even when the decoded
+            //   NSImage is already in the NSCache.
             do {
                 let data = try await matrixClient.client.getMediaContent(mediaSource: content.source)
                 imageData = data
+
+                let cacheKey = NSString(string: content.source.url())
+                if let cached = MatrixClient.imageCache.object(forKey: cacheKey) {
+                    image = Image(nsImage: cached)
+                    return
+                }
+
                 let nsImage = try data.toOrientedImage(contentType: contentType)
                 MatrixClient.setCachedImage(nsImage, forKey: cacheKey)
                 image = Image(nsImage: nsImage)