fix: inspect IOException immediate cause if there are no details in t…

…he exception (#159)

src/main/java/net/starschema/clouddb/jdbc/BQSQLException.java

@@ -176,7 +176,13 @@ private static String enrichReason(String reason, Throwable cause) {
         return prefix + googleJsonResponseException.getDetails().getMessage();
       }
     } else {
-      return prefix + cause.toString();
+      String throwableDetails = cause.toString();
+      // if the `cause` itself does not have a detailed message, ask for the message of its cause.
+      if (throwableDetails.isEmpty()) {
+        Throwable parentCause = cause.getCause();
+        if (parentCause != null) throwableDetails = parentCause.toString();
+      }
+      return prefix + throwableDetails;
     }
     return reason;
   }