Lib installer: factored out method to perform lib installation

The new method will be used in next commits to handle installations
of multiple libraries.
This commit fix also minor bug in progress bar.

Author: cmaglie

arduino-core/src/cc/arduino/contributions/libraries/LibraryInstaller.java

@@ -87,22 +87,31 @@ public synchronized void updateIndex(ProgressListener progressListener) throws E
   }
 
   public synchronized void install(ContributedLibrary lib, Optional<ContributedLibrary> mayReplacedLib, ProgressListener progressListener) throws Exception {
+    final MultiStepProgress progress = new MultiStepProgress(4);
+
+    // Do install library (3 steps)
+    performInstall(lib, mayReplacedLib, progressListener, progress);
+
+    // Rescan index (1 step)
+    rescanLibraryIndex(progress, progressListener);
+  }
+
+  private void performInstall(ContributedLibrary lib, Optional<ContributedLibrary> mayReplacedLib, ProgressListener progressListener, MultiStepProgress progress) throws Exception {
     if (lib.isLibraryInstalled()) {
       System.out.println(I18n.format(tr("Library is already installed: {0}:{1}"), lib.getName(), lib.getParsedVersion()));
       return;
     }
 
     DownloadableContributionsDownloader downloader = new DownloadableContributionsDownloader(BaseNoGui.librariesIndexer.getStagingFolder());
 
-    final MultiStepProgress progress = new MultiStepProgress(3);
-
     // Step 1: Download library
     try {
       downloader.download(lib, progress, I18n.format(tr("Downloading library: {0}"), lib.getName()), progressListener);
     } catch (InterruptedException e) {
       // Download interrupted... just exit
       return;
     }
+    progress.stepDone();
 
     // TODO: Extract to temporary folders and move to the final destination only
     // once everything is successfully unpacked. If the operation fails remove
@@ -129,9 +138,6 @@ public synchronized void install(ContributedLibrary lib, Optional<ContributedLib
     File destFolder = new File(libsFolder, lib.getName().replaceAll(" ", "_"));
     tmpFolder.renameTo(destFolder);
     progress.stepDone();
-
-    // Step 4: Rescan index
-    rescanLibraryIndex(progress, progressListener);
   }
 
   public synchronized void remove(ContributedLibrary lib, ProgressListener progressListener) throws IOException {