Fix #2670 (Xpath chapter detection wizard not working)

src/calibre/gui2/convert/xpath_wizard.py

@@ -31,6 +31,8 @@ class WizardWidget(QWidget, Ui_Form):
                 q = '[re:test(@%s, "%s", "i")]'%(attr, val)
             else:
                 q = '[@%s]'%attr
+        elif val:
+            q = '[re:test(., "%s", "i")]'%(val)
         expr = '//'+tag + q
         return expr