output/Interface: allow Pause() to throw exception

Coverity discovered that the Pulse plugin could throw exceptions from
Pause(), but that method was marked "noexcept" because its caller was
not designed to catch exceptions.  So instead of avoiding exceptions
(by catching and logging them in each and every implementation), let's
allow them, and do the catch/log game in the MPD core.

src/output/plugins/httpd/HttpdInternal.hxx

@@ -252,7 +252,7 @@ public:
 	void CancelAllClients();
 
 	void Cancel() noexcept override;
-	bool Pause() noexcept override;
+	bool Pause() override;
 
 private:
 	virtual void RunDeferred() override;

src/output/plugins/httpd/HttpdOutputPlugin.cxx

@@ -371,7 +371,7 @@ HttpdOutput::Play(const void *chunk, size_t size)
 }
 
 bool
-HttpdOutput::Pause() noexcept
+HttpdOutput::Pause()
 {
 	pause = true;