Fix a bug in SimbadClass.query_region_async()

It is now possible to specify multiple coordinates together with a
single radius as a `str`.

Author: eerovaher

astroquery/simbad/core.py

@@ -672,7 +672,8 @@ def query_region_async(self, coordinates, radius=2*u.arcmin,
             else:
                 frame = frame[0]
 
-            if isiterable(radius):
+            # `radius` as `str` is iterable, but contains only one value.
+            if isiterable(radius) and not isinstance(radius, str):
                 if len(radius) != len(ra):
                     raise ValueError("Mismatch between radii and coordinates")
             else: