Fix #11: local variable 'time_points' referenced before assignment

This fixes the issue #11 (closed) which were two related bugs:

• There was an assumption that if frequency_hz is present, then monotonic_time_points_us can not be present.
• There was a second assumption that if calendar_time_points is present, then monotonic_time_points_us must be present.

The way I understand the spec, both assumptions are invalid.

src/robofish/io/validation.py

@@ -113,9 +113,7 @@ def validate(iofile: File, strict_validate: bool = True) -> (bool, str):
                 if a in sampling:
                     assert_validate_type(sampling[a], a_type, a, f"sampling {s_name}")
 
-            if "frequency_hz" in sampling.attrs:
-                pass
-            elif "monotonic_time_points_us" in sampling:
+            if "monotonic_time_points_us" in sampling:
                 time_points = sampling["monotonic_time_points_us"]
                 # 1 dimensional array
                 assert_validate(
@@ -138,12 +136,13 @@ def validate(iofile: File, strict_validate: bool = True) -> (bool, str):
                     "Dimensionality of calendar_time_points should be 1",
                     f"sampling {s_name}",
                 )
-                assert_validate(
-                    calendar_points.shape[0] == time_points.shape[0],
-                    "The length of calendar points (%d) does not match the length of monotonic points (%d)"
-                    % (calendar_points.shape[0], time_points.shape[0]),
-                    f"sampling {s_name}",
-                )
+                if "monotonic_time_points_us" in sampling:
+                    assert_validate(
+                        calendar_points.shape[0] == time_points.shape[0],
+                        "The length of calendar points (%d) does not match the length of monotonic points (%d)"
+                        % (calendar_points.shape[0], time_points.shape[0]),
+                        f"sampling {s_name}",
+                    )
 
                 # validate iso8601, this validates the dtype implicitly
                 for c in calendar_points.asstr(encoding="utf-8"):