Restore guards (fix 'main' regression)

Author: WyattBlue

av/audio/fifo.py

@@ -192,15 +192,21 @@ def read_many(self, samples: cython.int, partial: cython.bint = False):
     @property
     def format(self):
         """The :class:`.AudioFormat` of this FIFO."""
+        if not self.ptr:
+            raise AttributeError(f"'{__name__}.AudioFifo' object has no attribute 'format'")
         return self.template.format
 
     @property
     def layout(self):
         """The :class:`.AudioLayout` of this FIFO."""
+        if not self.ptr:
+            raise AttributeError(f"'{__name__}.AudioFifo' object has no attribute 'layout'")
         return self.template.layout
 
     @property
     def sample_rate(self):
+        if not self.ptr:
+            raise AttributeError(f"'{__name__}.AudioFifo' object has no attribute 'sample_rate'")
         return self.template.sample_rate
 
     @property