add check for infinity in __call__ of EngFormatter

Author: swfiua

pandas/formats/format.py

@@ -2586,6 +2586,9 @@ def __call__(self, num):
         if decimal.Decimal.is_nan(dnum):
             return 'NaN'
 
+        if decimal.Decimal.is_infinite(dnum):
+            return 'inf'
+
         sign = 1
 
         if dnum < 0:  # pragma: no cover