Update src/client/streamableHttp.ts

nullish coalescing operator ?? instead of the logical OR operator || to handle the case where this?._eventSourceInit?.fetch or this._fetch might be null or undefined but not falsy

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

src/client/streamableHttp.ts

@@ -423,7 +423,7 @@ const response = await (this._fetch ?? fetch)(this._url, {
         signal: this._abortController?.signal,
       };
 
-      const response = await (this._fetch ?? fetch)(this._url, init);
+const response = await (this._fetch ?? fetch)(this._url, init);
 
       // Handle session ID received during initialization
       const sessionId = response.headers.get("mcp-session-id");