Fix reading Dragonfly non-OpenCell datasets with incomplete metadata (#…

…268)

* fallback if the same MM version is not used with opencell

* fallback for no positions

* fix type error

iohub/mmstack.py

@@ -219,7 +219,7 @@ def _set_mm_meta(self, mm_meta: dict) -> None:
         # acquisition script on the Dragonfly miroscope
         elif (
             mm_version == "2.0.1 20220920"
-            and self._mm_meta["Summary"]["Prefix"] == "raw_data"
+            and self._mm_meta["Summary"].get("Prefix", None) == "raw_data"
         ):
             files = natsorted(self.root.glob("*.ome.tif"))
             self.positions = len(files)  # not all positions are saved
@@ -238,7 +238,7 @@ def _set_mm_meta(self, mm_meta: dict) -> None:
                 self.channel_names.append(ch)
 
         else:
-            if self._mm_meta["Summary"]["Positions"] > 1:
+            if self._mm_meta["Summary"].get("Positions", 1) > 1:
                 self._stage_positions = []
 
                 for p in range(self._mm_meta["Summary"]["Positions"]):