Improve error handling for files on the commandline

Previously, any files that were specified on the commandline but could
not be opened were silently ignored. Only if --verify and --upload was
specified and _all_ files failed to open, a generic error message was
shown. Additionally, if multiple files were specified with --verify or
--upload, only the first would be acted on (the others would be openened
and shown in the GUI, but not actually verified or uploaded).

Now, whenever a file fails to open, an error message is shown (fatal
with --verify or --upload, non-fatal otherwise).

Furthermore, with --verify or --upload an error is shown when there is
not exactly one file on the commandline.

Finally, instead of keeping an "opened" variable, the code now just
checks the size of "editors" to see if a blank sketch should be opened.

app/src/processing/app/Base.java

@@ -318,7 +318,6 @@ public class Base {
     // Setup board-dependent variables.
     onBoardOrPortChange();
 
-    boolean opened = false;
     boolean doUpload = false;
     boolean doVerify = false;
     boolean doVerbose = false;
@@ -365,6 +364,9 @@ public class Base {
       filenames.add(args[i]);
     }
 
+    if ((doUpload || doVerify) && filenames.size() != 1)
+        showError(null, _("Must specify exactly one sketch file"), null);
+
     for (String path: filenames) {
       // Fix a problem with systems that use a non-ASCII languages. Paths are
       // being passed in with 8.3 syntax, which makes the sketch loader code
@@ -378,20 +380,22 @@ public class Base {
           e.printStackTrace();
         }
       }
+
       if (!new File(path).isAbsolute()) {
         path = new File(currentDirectory, path).getAbsolutePath();
       }
-      if (handleOpen(path) != null) {
-        opened = true;
+
+      if (handleOpen(path) == null) {
+        String mess = I18n.format(_("Failed to open sketch: \"{0}\""), path);
+        // Open failure is fatal in upload/verify mode
+        if (doUpload || doVerify)
+          showError(null, mess, null);
+        else
+          showWarning(null, mess, null);
       }
     }
 
     if (doUpload || doVerify) {
-      if (!opened) {
-        System.out.println(_("Can't open source sketch!"));
-        System.exit(2);
-      }
-
       // Set verbosity for command line build
       Preferences.set("build.verbose", "" + doVerbose);
       Preferences.set("upload.verbose", "" + doVerbose);
@@ -425,11 +429,10 @@ public class Base {
     }
 
     // Check if there were previously opened sketches to be restored
-    if (restoreSketches())
-      opened = true;
+    restoreSketches();
 
     // Create a new empty window (will be replaced with any files to be opened)
-    if (!opened) {
+    if (editors.isEmpty()) {
       handleNew();
     }