Don't let OME t_scale be equal to zero (#361)

* don't set t_scale to 0.0

* reformat z_step=0 warning

Author: ieivanov

iohub/mmstack.py

@@ -247,20 +247,24 @@ def _set_mm_meta(self, mm_meta: dict) -> None:
             for ch in self._mm_meta["Summary"].get("ChNames", []):
                 self.channel_names.append(ch)
         z_step_size = float(self._mm_meta["Summary"].get("z-step_um", 1.0))
-        if z_step_size == 0:
-            if self.slices == 1:
-                z_step_size = 1.0
-            else:
+        if z_step_size == 0.0:
+            z_step_size = 1.0
+            if self.slices != 1:
                 _logger.warning(
-                    f"Z-step size is {z_step_size} um in the metadata, "
-                    "Using 1.0 um instead."
+                    "Z-step size is set to 0.0 um in the metadata, "
+                    "using 1.0 um instead."
                 )
         self._z_step_size = z_step_size
         self.height = self._mm_meta["Summary"]["Height"]
         self.width = self._mm_meta["Summary"]["Width"]
-        self._t_scale = (
-            float(self._mm_meta["Summary"].get("Interval_ms", 1e3)) / 1e3
-        )
+        t_scale = float(self._mm_meta["Summary"].get("Interval_ms", 1e3)) / 1e3
+        if t_scale == 0.0:
+            t_scale = 1.0
+            _logger.warning(
+                "Time scale is set to 0.0 in the metadata, "
+                "using 1.0 instead."
+            )
+        self._t_scale = t_scale
 
     def _simplify_stage_position(self, stage_pos: dict):
         """