Fix xref and clarify edge case in Complex

Author: FilipToth

xml/System.Numerics/Complex.xml

@@ -2292,7 +2292,7 @@ A return value of `false` does not imply that <xref:System.Numerics.INumberBase%
 
 This function returns `true` for a complex number `a + bi` where `b` is zero.
 
-This function also returns `true` for <xref:System.Numerics.Infinity> and a complex number `a + bi` where `a` is infinity, but not `b`.
+This function also returns `true` for a complex number `a + bi` where `a` is infinity, but not `b`, and does not return true for <xref:System.Numerics.Complex.Infinity>.
 
           ]]></format>
         </remarks>