shared: ParallelDirScanner: Perform first pass to collect paths

Scan the top directory to collect paths for the threads. This
way we don't launch threads for paths without subdirs. Secondly,
large trees like usually $HOME will be scanned by multiple threads
at first.

Nevertheless, ParallelDirScanner can be improved still as threads may
run quickly out of work, so we may end up with only one anyway again

shared/paralleldirscanner.cpp

@@ -71,7 +71,34 @@ void ParallelDirScanner::scan()
 	this->targetPathsQueue.clear();
 	this->resultPathsQueue.clear();
 
-	this->targetPathsQueue.enqueue(this->paths);
+	/* First scan without subdirs. This way we collect paths for the threads */
+	WildcardMatcher matcher;
+	matcher.setPatterns(this->ignorePatterns);
+	for(QString &path : this->paths)
+	{
+		QDirIterator iterator(path, QStringList{}, QDir::Dirs | QDir::QDir::Files | QDir::NoDotDot);
+		while(iterator.hasNext())
+		{
+			QString path = iterator.next();
+			if(matcher.match(path))
+			{
+				continue;
+			}
+			QFileInfo info = iterator.fileInfo();
+			if(!info.isSymLink())
+			{
+				if(info.isDir())
+				{
+					this->targetPathsQueue.enqueue(info.absoluteFilePath());
+				}
+				else
+				{
+					this->resultPathsQueue.enqueue(info.absoluteFilePath());
+					this->processedPaths += 1;
+				}
+			}
+		}
+	}
 	int threadsNum = getThreadsNum();
 	if(threadsNum == 0)
 	{