fix FTDI required for SRM download bug

GC supports two download port types: serial ports and D2XX.  Before, if
either of these failed to load, the download dialog wouldn't show either
port type.  With this patch, if both fail, GC displays a warning, but if
either one succeeds, GC will proceed with only that port type.  This
change should fix the problem that users were having to download and
install both the FTDI drivers and the PL2303 ones in order to download
from the SRM PCV.

src/CommPort.cpp

@@ -33,15 +33,18 @@ CommPort::addListFunction(ListFunction f)
 QVector<CommPortPtr>
 CommPort::listCommPorts(QString &err)
 {
-    err = "";
+    QStringList errors;
     QVector<CommPortPtr> result;
     for (int i = 0; listFunctions && i < listFunctions->size(); ++i) {
-        QVector<CommPortPtr> tmp = (*listFunctions)[i](err);
-        if (err == "")
+        QString thisError = "";
+        QVector<CommPortPtr> tmp = (*listFunctions)[i](thisError);
+        if (thisError == "")
             result << tmp;
         else
-            err += "\n";
+            errors << thisError;
     }
+    if (result.isEmpty() && !errors.isEmpty())
+        err = errors.join("\n");
     return result;
 }
 

src/DownloadRideDialog.cpp

@@ -106,8 +106,8 @@ DownloadRideDialog::scanCommPorts()
     QString err;
     devList = CommPort::listCommPorts(err);
     if (err != "") {
-        QString msg = "Warning:\n\n" + err + "You may need to (re)install "
-            "the FTDI drivers before downloading.";
+        QString msg = "Warning(s):\n\n" + err + "\n\nYou may need to (re)install "
+            "the FTDI or PL2303 drivers before downloading.";
         QMessageBox::warning(0, "Error Loading Device Drivers", msg, 
                              QMessageBox::Ok, QMessageBox::NoButton);
     }

src/Serial.cpp

@@ -398,6 +398,8 @@ Serial::myListCommPorts(QString &err)
     QVector<CommPortPtr> result;
     char *devices[MAX_DEVICES];
     int devcnt = find_devices(devices, MAX_DEVICES);
+    if (devcnt == 0)
+        err = "No serial devices found.";
     for (int i = 0; i < devcnt; ++i) {
         result.append(CommPortPtr(new Serial(devices[i])));
         free(devices[i]);