lib/{curl,upnp}: add more exception handlers

Bugs found by Coverity.

src/lib/curl/Request.cxx

@@ -72,7 +72,7 @@ CurlRequest::~CurlRequest() noexcept
 }
 
 void
-CurlRequest::Start() noexcept
+CurlRequest::Start()
 {
 	assert(!registered);
 

src/lib/curl/Request.hxx

@@ -91,7 +91,7 @@ public:
 	 *
 	 * This method must be called in the event loop thread.
 	 */
-	void Start() noexcept;
+	void Start();
 
 	/**
 	 * Unregister this request via CurlGlobal::Remove().