LibAudio: Handle stream errors in FlacLoader

The FlacLoader already has numerous checks for invalid data reads and
for invalid stream states, but it never actually handles the stream
errors on the stream object. By handling them properly we can actually
run FuzzFlacLoader for longer than a few seconds before it hits the
first assertion :^).

Userland/Libraries/LibAudio/FlacLoader.h

@@ -22,11 +22,26 @@ class FlacInputStream : public Variant<Core::InputFileStream, InputMemoryStream>
 public:
     using Variant<Core::InputFileStream, InputMemoryStream>::Variant;
 
-    void seek(size_t pos)
+    bool seek(size_t pos)
     {
-        this->visit(
-            [&](auto& stream) {
+        return this->visit(
+            [&](Core::InputFileStream& stream) {
+                return stream.seek(pos);
+            },
+            [&](InputMemoryStream& stream) {
+                if (pos >= stream.bytes().size()) {
+                    return false;
+                }
                 stream.seek(pos);
+                return true;
+            });
+    }
+
+    bool handle_any_error()
+    {
+        return this->visit(
+            [&](auto& stream) {
+                return stream.handle_any_error();
             });
     }
 
@@ -56,6 +71,11 @@ class FlacLoaderPlugin : public LoaderPlugin {
 public:
     FlacLoaderPlugin(const StringView& path);
     FlacLoaderPlugin(const ByteBuffer& buffer);
+    ~FlacLoaderPlugin()
+    {
+        if (m_stream)
+            m_stream->handle_any_error();
+    }
 
     virtual bool sniff() override;