owpca: Use migrate_settings to fixup invalid variance_covered

`variance_covered` was persisted as a NaN value (gh-1897), causing a
TypeError in the widget's `__init__`.

Author: ales-erjavec

Orange/widgets/unsupervised/owpca.py

@@ -1,3 +1,5 @@
+import numbers
+
 from AnyQt.QtWidgets import QFormLayout, QLineEdit
 from AnyQt.QtGui import QColor
 from AnyQt.QtCore import Qt, QTimer
@@ -409,6 +411,20 @@ def send_report(self):
         ))
         self.report_plot()
 
+    @classmethod
+    def migrate_settings(cls, settings, version):
+        if "variance_covered" in settings:
+            # Due to the error in gh-1896 the variance_covered was persisted
+            # as a NaN value, causing a TypeError in the widgets `__init__`.
+            vc = settings["variance_covered"]
+            if isinstance(vc, numbers.Real):
+                if numpy.isfinite(vc):
+                    vc = int(vc)
+                else:
+                    vc = 100
+                settings["variance_covered"] = vc
+
+
 def main():
     import gc
     from AnyQt.QtWidgets import QApplication