Fix a couple of trivial issues in jsonb.c

Typo "aggreagate" appeared three times, and the return value of function
JsonbIteratorNext() was being assigned to an int variable in a bunch of
places.

Author: alvherre

src/backend/utils/adt/jsonb.c

@@ -372,7 +372,7 @@ JsonbToCString(StringInfo out, JsonbContainer *in, int estimated_len)
 {
 	bool		first = true;
 	JsonbIterator *it;
-	int			type = 0;
+	JsonbIteratorToken type;
 	JsonbValue	v;
 	int			level = 0;
 	bool		redo_switch = false;
@@ -454,7 +454,7 @@ JsonbToCString(StringInfo out, JsonbContainer *in, int estimated_len)
 				first = false;
 				break;
 			default:
-				elog(ERROR, "unknown flag of jsonb iterator");
+				elog(ERROR, "unknown jsonb iterator token type");
 		}
 	}