[WebGPU] GPUBuffer.destroy does not need to perform an unmap on an em…

…pty buffer

https://bugs.webkit.org/show_bug.cgi?id=265433
<radar://118866396>

Reviewed by Dan Glastonbury.

GPUBuffer.destroy should be a no-op if the buffer was never mapped.

* Source/WebCore/Modules/WebGPU/GPUBuffer.cpp:
(WebCore::GPUBuffer::destroy):

Canonical link: https://commits.webkit.org/271245@main

Source/WebCore/Modules/WebGPU/GPUBuffer.cpp

@@ -145,6 +145,9 @@ void GPUBuffer::internalUnmap(ScriptExecutionContext& scriptExecutionContext)
 
 void GPUBuffer::destroy(ScriptExecutionContext& scriptExecutionContext)
 {
+    if (!m_bufferSize)
+        return;
+
     internalUnmap(scriptExecutionContext);
     m_bufferSize = 0;
     m_backing->destroy();