fix switching to artist info screen

if one switched from artist info screen while artist info was being
downloaded, {s,}he wouldn't be able to enter the screen again.

src/lastfm.cpp

@@ -214,7 +214,7 @@ void Lastfm::Refetch()
 
 bool Lastfm::SetArtistInfoArgs(const std::string &artist, const std::string &lang)
 {
-	if (isDownloadInProgress)
+	if (isDownloading())
 		return false;
 	
 	itsService.reset(new ArtistInfo);

src/lastfm.h

@@ -53,6 +53,7 @@ class Lastfm : public Screen<Scrollpad>
 		
 		void Refetch();
 		
+		bool isDownloading() { return isDownloadInProgress && !isReadyToTake; }
 		bool SetArtistInfoArgs(const std::string &artist, const std::string &lang = "");
 		
 	protected:

src/ncmpcpp.cpp

@@ -2142,7 +2142,7 @@ int main(int argc, char *argv[])
 #		ifdef HAVE_CURL_CURL_H
 		else if (Keypressed(input, Key.ArtistInfo))
 		{
-			if (myScreen == myLastfm)
+			if (myScreen == myLastfm || myLastfm->isDownloading())
 			{
 				myLastfm->SwitchTo();
 				continue;