Fix misleading log messages in WiFi endpoint RPC response handling

[Copilot]

After switching to !response.empty() guards, the else branches in Device_WiFi_EndPoint.cpp still logged "curl init failed" — inaccurate since an empty response from getJsonRPCData() can result from RPC-level failures unrelated to curl initialization.

Changes

• Device_WiFi_EndPoint.cpp: Replaced all three occurrences of "curl init failed" in else branches following !response.empty() checks with "getJsonRPCData() failed or returned empty response"

// Before
RDK_LOG(RDK_LOG_ERROR, LOG_TR69HOSTIF, "%s: curl init failed\n", __FUNCTION__);

// After
RDK_LOG(RDK_LOG_ERROR, LOG_TR69HOSTIF, "%s: getJsonRPCData() failed or returned empty response\n", __FUNCTION__);

Applies to all three RPC call sites: GetWiFiSignalStrength, GetConnectedSSID, and the initial endpoint query.

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