fix: raise error if empty header

Author: YodaEmbedding

pyntcloud/io/off.py

@@ -12,6 +12,7 @@ def read_off(filename):
         if "OFF" not in first_line:
             raise ValueError("The file does not start with the word OFF")
         has_color = "C" in first_line
+        num_rows = None
 
         # Read header.
         for line in f:
@@ -25,6 +26,9 @@ def read_off(filename):
             num_rows = n_points + n_faces
             break
 
+        if num_rows is None:
+            raise ValueError("The file does not contain a valid header")
+
         # Read remaining lines.
         lines = [next(f) for _ in range(num_rows)]