If CUPS has no default printer, set up the first one in list

Otherwise QCUPSSupport is instantiated without any printer being set up,
which leads to bugs and/or crashes in other parts using QCUPSSupport.

Change-Id: I1f4ddde5a28d6448d78aed856104ce8448e213c7
Reviewed-by: John Layt <jlayt@kde.org>

src/printsupport/kernel/qcups.cpp

@@ -144,11 +144,13 @@ QCUPSSupport::QCUPSSupport()
     for (int i = 0; i <  prnCount; ++i) {
         if (printers[i].is_default) {
             currPrinterIndex = i;
-            setCurrentPrinter(i);
             break;
         }
     }
 
+    if (prnCount > 0)
+        setCurrentPrinter(currPrinterIndex);
+
 #ifndef QT_NO_TEXTCODEC
     cups_lang_t *cupsLang = _cupsLangGet(0);
     codec = QTextCodec::codecForName(_cupsLangEncoding(cupsLang));