neuprint: If the segmentation layer has multiple sources, assume we w…

…ant the first one.

navis/interfaces/neuprint.py

@@ -577,13 +577,23 @@ def get_seg_source(*, client=None):
     if len(named_segs):
         segs = named_segs
 
-    # Get the first entry
+    # If there are multiple segmentation layers, select the first entry
     seg_source = segs[0]['source']
 
-    # Make sure it's actually a string and not a {'source': url, 'subsources'...} dict
+    # If there are multiple segmentation sources for
+    # the layer we picked, select the first source.
+    if isinstance(seg_source, list):
+        seg_source = seg_source[0]
+
+    # If it's a dict like {'source': url, 'subsources'...},
+    # select the url.
     if isinstance(seg_source, dict):
         seg_source = seg_source['url']
 
+    if not isinstance(seg_source, str):
+        e = f"Could not understand segmentation source: {seg_source}"
+        raise RuntimeError(e)
+
     if len(segs) > 1:
         logger.warning(f'{len(segs)} segmentation sources found. Using the '
                        f'first entry: "{seg_source}"')