[FIX] wrong handling of border.rectList with PySide6 backend

This appears to fix the problems described in issue #102 .
The changes can be made more pythonic, this patch literally came out
of my debugging session - feedback regarding cleaning it up and
making it ready for merging would be highly appreciated

Author: martinschwinzerl

qwt/plot_canvas.py

@@ -75,9 +75,16 @@ def drawRects(self, rects, count):
             # Pyside
             if isinstance(rects, (QRect, QRectF)):
                 self.border.list = [rects]
+            elif all(isinstance(rects, (QRect, QRectF)):
+                if isinstance(rects, list):
+                    self.border.rectList += rects
+                else:
+                    # That may not even be necessary
+                    self.border.rectList += [r for r in rects]
             else:
+                # Should we get here ?
                 for i in range(count):
-                    self.border.rectList += [rects.getRect().index(i)]
+                    self.border.rectList += [rects[i]]
         else:
             # PyQt
             for i in range(count):