fix: prevent 500 error when course mode currency is not the same as the one configured in settings (#31312)

This commit solves the http 500 error when course concurrency is setted different for PAID_COURSE_REGISTRATION_CURRENCY and course modes.

common/djangoapps/course_modes/models.py

@@ -774,7 +774,10 @@ class CourseMode(models.Model):
         If there is no mode found, will return the price of DEFAULT_MODE, which is 0
         """
         modes = cls.modes_for_course(course_id)
-        return min(mode.min_price for mode in modes if mode.currency.lower() == currency.lower())
+        return min(
+            (mode.min_price for mode in modes if mode.currency.lower() == currency.lower()),
+            default=0
+        )
 
     @classmethod
     def is_eligible_for_certificate(cls, mode_slug, status=None):