QApplication: replace some sneaky code with a strategic goto

Instead of replacing the container iterated over, in the middle
of the loop body(!), place a label in front of the loop and
use goto to restart the entire loop.

This allows to mark the variable 'list' const, which is a
prerequesite for replacing the loop with a C++11 range-for
one.

But it also makes the code less cryptic. No-one expects the
container to be re-seated in the middle of the loop.

The compiler agrees: saves 144b of text size on optimized
AMD64 GCC 4.9 Linux builds.

Change-Id: I22d07672a1bbe9d7ffb083ae231eda760c29d350
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

src/widgets/kernel/qapplication.cpp

@@ -1905,6 +1905,7 @@ bool QApplicationPrivate::tryCloseAllWidgetWindows(QWindowList *processedWindows
             processedWindows->append(window);
     }
 
+retry:
     QWidgetList list = QApplication::topLevelWidgets();
     for (int i = 0; i < list.size(); ++i) {
         QWidget *w = list.at(i);
@@ -1915,8 +1916,7 @@ bool QApplicationPrivate::tryCloseAllWidgetWindows(QWindowList *processedWindows
                 return false;
             if (window)
                 processedWindows->append(window);
-            list = QApplication::topLevelWidgets();
-            i = -1;
+            goto retry;
         }
     }
     return true;