fix: Fix coverRendered flag (#1154)

## Summary

* **What is the goal of this PR?** During low memory situations (which I
encounterde a lot during my recent bugfixing activities) a cover was
considered rendered even if the buffer could not be stored.
* **What changes are included?** Proper assignment of flag logic

## Additional Context
-

---

### AI Usage

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please be transparent about their usage as it
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Did you use AI tools to help write this code? _**NO**_

src/components/themes/BaseTheme.cpp

@@ -424,7 +424,7 @@ void BaseTheme::drawRecentBookCover(GfxRenderer& renderer, Rect rect, const std:
 
           // Store the buffer with cover image for fast navigation
           coverBufferStored = storeCoverBuffer();
-          coverRendered = true;
+          coverRendered = coverBufferStored;  // Only consider it rendered if we successfully stored the buffer
 
           // First render: if selected, draw selection indicators now
           if (bookSelected) {

src/components/themes/lyra/Lyra3CoversTheme.cpp

@@ -79,7 +79,7 @@ void Lyra3CoversTheme::drawRecentBookCover(GfxRenderer& renderer, Rect rect, con
       }
 
       coverBufferStored = storeCoverBuffer();
-      coverRendered = true;
+      coverRendered = coverBufferStored;  // Only consider it rendered if we successfully stored the buffer
     }
 
     for (int i = 0; i < std::min(static_cast<int>(recentBooks.size()), Lyra3CoversMetrics::values.homeRecentBooksCount);

src/components/themes/lyra/LyraTheme.cpp

@@ -464,7 +464,7 @@ void LyraTheme::drawRecentBookCover(GfxRenderer& renderer, Rect rect, const std:
       }
 
       coverBufferStored = storeCoverBuffer();
-      coverRendered = true;
+      coverRendered = coverBufferStored;  // Only consider it rendered if we successfully stored the buffer
     }
 
     bool bookSelected = (selectorIndex == 0);